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august 1990 order number: 231456-006 8088 8-bit hmos microprocessor 8088/8088-2 y 8-bit data bus interface y 16-bit internal architecture y direct addressing capability to 1 mbyte of memory y direct software compatibility with 8086 cpu y 14-word by 16-bit register set with symmetrical operations y 24 operand addressing modes y byte, word, and block operations y 8-bit and 16-bit signed and unsigned arithmetic in binary or decimal, including multiply and divide y two clock rates: e 5 mhz for 8088 e 8 mhz for 8088-2 y available in express e standard temperature range e extended temperature range the intel 8088 is a high performance microprocessor implemented in n-channel, depletion load, silicon gate technology (hmos-ii), and packaged in a 40-pin cerdip package. the processor has attributes of both 8- and 16-bit microprocessors. it is directly compatible with 8086 software and 8080/8085 hardware and periph- erals. 231456 1 figure 1. 8088 cpu functional block diagram 231456 2 figure 2. 8088 pin configuration
8088 table 1. pin description the following pin function descriptions are for 8088 systems in either minimum or maximum mode. the ``local bus'' in these descriptions is the direct multiplexed bus interface connection to the 8088 (without regard to additional bus buffers). symbol pin no. type name and function ad7 ad0 9 16 i/o address data bus: these lines constitute the time multiplexed memory/io address (t1) and data (t2, t3, tw, t4) bus. these lines are active high and float to 3-state off during interrupt acknowledge and local bus ``hold acknowledge''. a15a8 28, 39 o address bus: these lines provide address bits 8 through 15 for the entire bus cycle (t1 t4). these lines do not have to be latched by ale to remain valid. a15 a8 are active high and float to 3-state off during interrupt acknowledge and local bus ``hold acknowledge''. a17/s4, a16/s3 a19/s6, a18/s5, 35 38 o address/status: during t1, these are the four most significant address lines for memory operations. during i/o operations, these lines are low. during memory and i/o operations, status information is available on these lines during t2, t3, tw, and t4. s6 is always low. the status of the interrupt enable flag bit (s5) is updated at the beginning of each clock cycle. s4 and s3 are encoded as shown. this information indicates which segment register is presently being used for data accessing. these lines float to 3-state off during local bus ``hold acknowledge''. s4 s3 characteristics 0 (low) 0 alternate data 0 1 stack 1 (high) 0 code or none 1 1 data s6 is 0 (low) rd 32 o read: read strobe indicates that the processor is performing a memory or i/o read cycle, depending on the state of the io/m pin or s2. this signal is used to read devices which reside on the 8088 local bus. rd is active low during t2, t3 and tw of any read cycle, and is guaranteed to remain high in t2 until the 8088 local bus has floated. this signal floats to 3-state off in ``hold acknowledge''. ready 22 i ready: is the acknowledgement from the addressed memory or i/o device that it will complete the data transfer. the rdy signal from memory or i/o is synchronized by the 8284 clock generator to form ready. this signal is active high. the 8088 ready input is not synchronized. correct operation is not guaranteed if the set up and hold times are not met. intr 18 i interrupt request: is a level triggered input which is sampled during the last clock cycle of each instruction to determine if the processor should enter into an interrupt acknowledge operation. a subroutine is vectored to via an interrupt vector lookup table located in system memory. it can be internally masked by software resetting the interrupt enable bit. intr is internally synchronized. this signal is active high. test 23 i test : input is examined by the ``wait for test'' instruction. if the test input is low, execution continues, otherwise the processor waits in an ``idle'' state. this input is synchronized internally during each clock cycle on the leading edge of clk. 2
8088 table 1. pin description (continued) symbol pin no. type name and function nmi 17 i non-maskable interrupt: is an edge triggered input which causes a type 2 interrupt. a subroutine is vectored to via an interrupt vector lookup table located in system memory. nmi is not maskable internally by software. a transition from a low to high initiates the interrupt at the end of the current instruction. this input is internally synchronized. reset 21 i reset: causes the processor to immediately terminate its present activity. the signal must be active high for at least four clock cycles. it restarts execution, as described in the instruction set description, when reset returns low. reset is internally synchronized. clk 19 i clock: provides the basic timing for the processor and bus controller. it is asymmetric with a 33% duty cycle to provide optimized internal timing. v cc 40 v cc : is the a 5v g 10% power supply pin. gnd 1, 20 gnd: are the ground pins. mn/mx 33 i minimum/maximum: indicates what mode the processor is to operate in. the two modes are discussed in the following sections. the following pin function descriptions are for the 8088 minimum mode (i.e., mn/mx e v cc ). only the pin functions which are unique to minimum mode are described; all other pin functions are as described above. symbol pin no. type name and function io/m 28 o status line: is an inverted maximum mode s2 . it is used to distinguish a memory access from an i/o access. io/m becomes valid in the t4 preceding a bus cycle and remains valid until the final t4 of the cycle (i/o e high, m e low). io/m floats to 3-state off in local bus ``hold acknowledge''. wr 29 o write: strobe indicates that the processor is performing a write memory or write i/o cycle, depending on the state of the io/m signal. wr is active for t2, t3, and tw of any write cycle. it is active low, and floats to 3-state off in local bus ``hold acknowledge''. inta 24 o inta: is used as a read strobe for interrupt acknowledge cycles. it is active low during t2, t3, and tw of each interrupt acknowledge cycle. ale 25 o address latch enable: is provided by the processor to latch the address into an address latch. it is a high pulse active during clock low of t1 of any bus cycle. note that ale is never floated. dt/r 27 o data transmit/receive: is needed in a minimum system that desires to use a data bus transceiver. it is used to control the direction of data flow through the transceiver. logically, dt/r is equivalent to s1 in the maximum mode, and its timing is the same as for io/m (t e high, r e low). this signal floats to 3-state off in local ``hold acknowledge''. den 26 o data enable: is provided as an output enable for the data bus transceiver in a minimum system which uses the transceiver. den is active low during each memory and i/o access, and for inta cycles. for a read or inta cycle, it is active from the middle of t2 until the middle of t4, while for a write cycle, it is active from the beginning of t2 until the middle of t4. den floats to 3-state off during local bus ``hold acknowledge''. 3
8088 table 1. pin description (continued) symbol pin no. type name and function hold, hlda 31, 30 i, o hold: indicates that another master is requesting a local bus ``hold''. to be acknowledged, hold must be active high. the processor receiving the ``hold'' request will issue hlda (high) as an acknowledgement, in the middle of a t4 or ti clock cycle. simultaneous with the issuance of hlda the processor will float the local bus and control lines. after hold is detected as being low, the processor lowers hlda, and when the processor needs to run another cycle, it will again drive the local bus and control lines. hold and hlda have internal pull-up resistors. hold is not an asynchronous input. external synchronization should be provided if the system cannot otherwise guarantee the set up time. sso 34 o status line: is logically equivalent to so in the maximum mode. the combination of sso , io/m and dt/r allows the system to completely decode the current bus cycle status. io/m dt/r sso characteristics 1(high) 0 0 interrupt acknowledge 1 0 1 read i/o port 1 1 0 write i/o port 1 1 1 halt 0(low) 0 0 code access 0 0 1 read memory 0 1 0 write memory 0 1 1 passive the following pin function descriptions are for the 8088/8288 system in maximum mode (i.e., mn/mx e gnd). only the pin functions which are unique to maximum mode are described; all other pin functions are as described above. symbol pin no. type name and function s2 ,s1 ,s0 2628 o status: is active during clock high of t4, t1, and t2, and is returned to the passive state (1,1,1) during t3 or during tw when ready is high. this status is used by the 8288 bus controller to generate all memory and i/o access control signals. any change by s2 ,s1 ,ors0 during t4 is used to indicate the beginning of a bus cycle, and the return to the passive state in t3 and tw is used to indicate the end of a bus cycle. these signals float to 3-state off during ``hold acknowledge''. during the first clock cycle after reset becomes active, these signals are active high. after this first clock, they float to 3-state off. s2 s1 s0 characteristics 0(low) 0 0 interrupt acknowledge 0 0 1 read i/o port 0 1 0 write i/o port 0 1 1 halt 1(high) 0 0 code access 1 0 1 read memory 1 1 0 write memory 1 1 1 passive 4
8088 table 1. pin description (continued) symbol pin no. type name and function rq /gt0 , rq /gt1 30, 31 i/o request/grant: pins are used by other local bus masters to force the processor to release the local bus at the end of the processor's current bus cycle. each pin is bidirectional with rq /gt0 having higher priority than rq / gt1 .rq /gt has an internal pull-up resistor, so may be left unconnected. the request/grant sequence is as follows (see figure 8): 1. a pulse of one clk wide from another local bus master indicates a local bus request (``hold'') to the 8088 (pulse 1). 2. during a t4 or ti clock cycle, a pulse one clock wide from the 8088 to the requesting master (pulse 2), indicates that the 8088 has allowed the local bus to float and that it will enter the ``hold acknowledge'' state at the next clk. the cpu's bus interface unit is disconnected logically from the local bus during ``hold acknowledge''. the same rules as for hold/holda apply as for when the bus is released. 3. a pulse one clk wide from the requesting master indicates to the 8088 (pulse 3) that the ``hold'' request is about to end and that the 8088 can reclaim the local bus at the next clk. the cpu then enters t4. each master-master exchange of the local bus is a sequence of three pulses. there must be one idle clk cycle after each bus exchange. pulses are active low. if the request is made while the cpu is performing a memory cycle, it will release the local bus during t4 of the cycle when all the following conditions are met: 1. request occurs on or before t2. 2. current cycle is not the low bit of a word. 3. current cycle is not the first acknowledge of an interrupt acknowledge sequence. 4. a locked instruction is not currently executing. if the local bus is idle when the request is made the two possible events will follow: 1. local bus will be released during the next clock. 2. a memory cycle will start within 3 clocks. now the four rules for a currently active memory cycle apply with condition number 1 already satisfied. lock 29 o lock : indicates that other system bus masters are not to gain control of the system bus while lock is active (low). the lock signal is activated by the ``lock'' prefix instruction and remains active until the completion of the next instruction. this signal is active low, and floats to 3-state off in ``hold acknowledge''. qs1, qs0 24, 25 o queue status: provide status to allow external tracking of the internal 8088 instruction queue. the queue status is valid during the clk cycle after which the queue operation is performed. qs1 qs0 characteristics 0(low) 0 no operation 0 1 first byte of opcode from queue 1(high) 0 empty the queue 1 1 subsequent byte from queue e 34 o pin 34 is always high in the maximum mode. 5
8088 231456 3 figure 3. memory organization functional description memory organization the processor provides a 20-bit address to memory which locates the byte being referenced. the memo- ry is organized as a linear array of up to 1 million bytes, addressed as 00000(h) to fffff(h). the memory is logically divided into code, data, extra data, and stack segments of up to 64k bytes each, with each segment falling on 16-byte boundaries (see figure 3). all memory references are made relative to base ad- dresses contained in high speed segment registers. the segment types were chosen based on the ad- dressing needs of programs. the segment register to be selected is automatically chosen according to the rules of the following table. all information in one segment type share the same logical attributes (e.g. code or data). by structuring memory into relocat- able areas of similar characteristics and by automati- cally selecting segment registers, programs are shorter, faster, and more structured. word (16-bit) operands can be located on even or odd address boundaries. for address and data oper- ands, the least significant byte of the word is stored in the lower valued address location and the most significant byte in the next higher address location. the biu will automatically execute two fetch or write cycles for 16-bit operands. memory segment segment selection rule reference used register used instructions code (cs) automatic with all instruction prefetch. stack stack (ss) all stack pushes and pops. memory references relative to bp base register except data references. local data data (ds) data references when: relative to stack, destination of string operation, or explicity overridden. external (global) data extra (es) destination of string operations: explicitly selected using a segment override. 6
8088 certain locations in memory are reserved for specific cpu operations (see figure 4). locations from ad- dresses ffff0h through fffffh are reserved for operations including a jump to the initial system ini- tialization routine. following reset, the cpu will al- ways begin execution at location ffff0h where the jump must be located. locations 00000h through 003ffh are reserved for interrupt operations. four- byte pointers consisting of a 16-bit segment address and a 16-bit offset address direct program flow to one of the 256 possible interrupt service routines. the pointer elements are assumed to have been stored at their respective places in reserved memory prior to the occurrence of interrupts. minimum and maximum modes the requirements for supporting minimum and maxi- mum 8088 systems are sufficiently different that they cannot be done efficiently with 40 uniquely de- fined pins. consequently, the 8088 is equipped with a strap pin (mn/mx ) which defines the system con- 231456 4 figure 4. reserved memory locations figuration. the definition of a certain subset of the pins changes, dependent on the condition of the strap pin. when the mn/mx pin is strapped to gnd, the 8088 defines pins 24 through 31 and 34 in maxi- mum mode. when the mn/mx pin is strapped to v cc , the 8088 generates bus control signals itself on pins 24 through 31 and 34. the minimum mode 8088 can be used with either a multiplexed or demultiplexed bus. the multiplexed bus configuration is compatible with the mcs-85 multiplexed bus peripherals. this configuration (see figure 5) provides the user with a minimum chip count system. this architecture provides the 8088 processing power in a highly integrated form. the demultiplexed mode requires one latch (for 64k addressability) or two latches (for a full megabyte of addressing). a third latch can be used for buffering if the address bus loading requires it. a transceiver can also be used if data bus buffering is required (see figure 6). the 8088 provides den and dt/r to control the transceiver, and ale to latch the ad- dresses. this configuration of the minimum mode provides the standard demultiplexed bus structure with heavy bus buffering and relaxed bus timing re- quirements. the maximum mode employs the 8288 bus control- ler (see figure 7). the 8288 decodes status lines s0 ,s1 , and s2 , and provides the system with all bus control signals. moving the bus control to the 8288 provides better source and sink current capability to the control lines, and frees the 8088 pins for extend- ed large system features. hardware lock, queue status, and two request/grant interfaces are provid- ed by the 8088 in maximum mode. these features allow co-processors in local bus and remote bus configurations. 7
8088 231456 5 figure 5. multiplexed bus configuration 8
8088 231456 6 figure 6. demultiplexed bus configuration 231456 7 figure 7. fully buffered system using bus controller 9
8088 bus operation the 8088 address/data bus is broken into three partsethe lower eight address/data bits (ad0 ad7), the middle eight address bits (a8 a15), and the upper four address bits (a16 a19). the ad- dress/data bits and the highest four address bits are time multiplexed. this technique provides the most efficient use of pins on the processor, permitting the use of a standard 40 lead package. the middle eight address bits are not multiplexed, i.e. they remain val- id throughout each bus cycle. in addition, the bus can be demultiplexed at the processor with a single address latch if a standard, non-multiplexed bus is desired for the system. each processor bus cycle consists of at least four clk cycles. these are referred to as t1, t2, t3, and t4 (see figure 8). the address is emitted from the processor during t1 and data transfer occurs on the bus during t3 and t4. t2 is used primarily for chang- 231456 8 figure 8. basic system timing 10
8088 ing the direction of the bus during read operations. in the event that a ``not ready'' indication is given by the addressed device, ``wait'' states (tw) are in- serted between t3 and t4. each inserted ``wait'' state is of the same duration as a clk cycle. periods can occur between 8088 driven bus cycles. these are referred to as ``idle'' states (ti), or inactive clk cycles. the processor uses these cycles for internal housekeeping. during t1 of any bus cycle, the ale (address latch enable) signal is emitted (by either the processor or the 8288 bus controller, depending on the mn/mx strap). at the trailing edge of this pulse, a valid ad- dress and certain status information for the cycle may be latched. status bits s0 ,s1 , and s2 are used by the bus con- troller, in maximum mode, to identify the type of bus transaction according to the following table: s2 s1 s0 characteristics 0(low) 0 0 interrupt acknowledge 0 0 1 read i/o 0 1 0 write i/o 0 1 1 halt 1(high) 0 0 instruction fetch 1 0 1 read data from memory 1 1 0 write data to memory 1 1 1 passive (no bus cycle) status bits s3 through s6 are multiplexed with high order address bits and are therefore valid during t2 through t4. s3 and s4 indicate which segment reg- ister was used for this bus cycle in forming the ad- dress according to the following table: s 4 s 3 characteristics 0(low) 0 alternate data (extra segment) 0 1 stack 1(high) 0 code or none 1 1 data s5 is a reflection of the psw interrupt enable bit. s6 is always equal to 0. i/o addressing in the 8088, i/o operations can address up to a maximum of 64k i/o registers. the i/o address ap- pears in the same format as the memory address on bus lines a15 a0. the address lines a19 a16 are zero in i/o operations. the variable i/o instructions, which use register dx as a pointer, have full address capability, while the direct i/o instructions directly address one or two of the 256 i/o byte locations in page 0 of the i/o address space. i/o ports are ad- dressed in the same manner as memory locations. designers familiar with the 8085 or upgrading an 8085 design should note that the 8085 addresses i/o with an 8-bit address on both halves of the 16- bit address bus. the 8088 uses a full 16-bit address on its lower 16 address lines. external interface processor reset and initialization processor initialization or start up is accomplished with activation (high) of the reset pin. the 8088 reset is required to be high for greater than four clock cycles. the 8088 will terminate operations on the high-going edge of reset and will remain dor- mant as long as reset is high. the low-going transition of reset triggers an internal reset se- quence for approximately 7 clock cycles. after this interval the 8088 operates normally, beginning with the instruction in absolute locations ffff0h (see figure 4). the reset input is internally synchroniz- ed to the processor clock. at initialization, the high to low transition of reset must occur no sooner than 50 m s after power up, to allow complete initiali- zation of the 8088. nmi asserted prior to the 2nd clock after the end of reset will not be honored. if nmi is asserted after that point and during the internal reset sequence, the processor may execute one instruction before responding to the interrupt. a hold request active immediately after reset will be honored before the first instruction fetch. all 3-state outputs float to 3-state off during reset. status is active in the idle state for the first clock after reset becomes active and then floats to 3-state off. ale and hlda are driven low. interrupt operations interrupt operations fall into two classes: software or hardware initiated. the software initiated interrupts and software aspects of hardware interrupts are specified in the instruction set description in the iapx 88 book or the iapx 86,88 user's manual. hardware interrupts can be classified as nonmaska- ble or maskable. 11
8088 interrupts result in a transfer of control to a new pro- gram location. a 256 element table containing ad- dress pointers to the interrupt service program loca- tions resides in absolute locations 0 through 3ffh (see figure 4), which are reserved for this purpose. each element in the table is 4 bytes in size and cor- responds to an interrupt ``type.'' an interrupting de- vice supplies an 8-bit type number, during the inter- rupt acknowledge sequence, which is used to vector through the appropriate element to the new interrupt service program location. non-maskable interrupt (nmi) the processor provides a single non-maskable inter- rupt (nmi) pin which has higher priority than the maskable interrupt request (intr) pin. a typical use would be to activate a power failure routine. the nmi is edge-triggered on a low to high transition. the activation of this pin causes a type 2 interrupt. nmi is required to have a duration in the high state of greater than two clock cycles, but is not required to be synchronized to the clock. any higher going transition of nmi is latched on-chip and will be serv- iced at the end of the current instruction or between whole moves (2 bytes in the case of word moves) of a block type instruction. worst case response to nmi would be for multiply, divide, and variable shift instructions. there is no specification on the occur- rence of the low-going edge; it may occur before, during, or after the servicing of nmi. another high- going edge triggers another response if it occurs af- ter the start of the nmi procedure. the signal must be free of logical spikes in general and be free of bounces on the low-going edge to avoid triggering extraneous responses. maskable interrupt (intr) the 8088 provides a single interrupt request input (intr) which can be masked internally by software with the resetting of the interrupt enable (if) flag bit. the interrupt request signal is level triggered. it is internally synchronized during each clock cycle on the high-going edge of clk. to be responded to, intr must be present (high) during the clock peri- od preceding the end of the current instruction or the end of a whole move for a block type instruction. during interrupt response sequence, further inter- rupts are disabled. the enable bit is reset as part of the response to any interrupt (intr, nmi, software interrupt, or single step), although the flags regis- ter which is automatically pushed onto the stack re- flects the state of the processor prior to the inter- rupt. until the old flags register is restored, the enable bit will be zero unless specifically set by an instruction. during the response sequence (see figure 9), the processor executes two successive (back to back) interrupt acknowledge cycles. the 8088 emits the lock signal (maximum mode only) from t2 of the first bus cycle until t2 of the second. a local bus ``hold'' request will not be honored until the end of the second bus cycle. in the second bus cycle, a byte is fetched from the external interrupt system (e.g., 8259a pic) which identifies the source (type) of the interrupt. this byte is multiplied by four and used as a pointer into the interrupt vector lookup table. an intr signal left high will be continually responded to within the limitations of the enable bit and sample period. the interrupt return instruction includes a flags pop which returns the status of the original interrupt enable bit when it restores the flags. halt when a software halt instruction is executed, the processor indicates that it is entering the halt state in one of two ways, depending upon which mode is strapped. in minimum mode, the processor issues ale, delayed by one clock cycle, to allow the sys- tem to latch the halt status. halt status is available on io/m , dt/r , and sso . in maximum mode, the processor issues appropriate halt status on s2 , s1 , and s0 , and the 8288 bus controller issues one ale. the 8088 will not leave the halt state when a local bus hold is entered while in halt. in this case, the processor reissues the halt indicator at the end of the local bus hold. an interrupt request or reset will force the 8088 out of the halt state. read/modify/write (semaphore) operations via lock the lock status information is provided by the processor when consecutive bus cycles are required during the execution of an instruction. this allows the processor to perform read/modify/write opera- tions on memory (via the ``exchange register with memory'' instruction), without another system bus master receiving intervening memory cycles. this is useful in multiprocessor system configurations to ac- complish ``test and set lock'' operations. the lock signal is activated (low) in the clock cycle following decoding of the lock prefix instruction. it is deacti- vated at the end of the last bus cycle of the instruc- tion following the lock prefix. while lock is active, a request on a rq /gt pin will be recorded, and then honored at the end of the lock. 12
8088 231456 9 figure 9. interrupt acknowledge sequence external synchronization via test as an alternative to interrupts, the 8088 provides a single software-testable input pin (test ). this input is utilized by executing a wait instruction. the sin- gle wait instruction is repeatedly executed until the test input goes active (low). the execution of wait does not consume bus cycles once the queue is full. if a local bus request occurs during wait execution, the 8088 3-states all output drivers. if interrupts are enabled, the 8088 will recognize interrupts and pro- cess them. the wait instruction is then refetched, and reexecuted. basic system timing in minimum mode, the mn/mx pin is strapped to v cc and the processor emits bus control signals compatible with the 8085 bus structure. in maximum mode, the mn/mx pin is strapped to gnd and the processor emits coded status information which the 8288 bus controller uses to generate multibus compatible bus control signals. system timingeminimum system (see figure 8) the read cycle begins in t1 with the assertion of the address latch enable (ale) signal. the trailing (low going) edge of this signal is used to latch the ad- dress information, which is valid on the address/ data bus (ad0 ad7) at this time, into the 8282/8283 latch. address lines a8 through a15 do not need to be latched because they remain valid throughout the bus cycle. from t1 to t4 the io/m signal indicates a memory or i/o operation. at t2 the address is removed from the address/data bus and the bus goes to a high impedance state. the read control signal is also asserted at t2. the read (rd ) signal causes the addressed device to enable its data bus drivers to the local bus. some time later, valid data will be available on the bus and the ad- dressed device will drive the ready line high. when the processor returns the read signal to a high level, the addressed device will again 3-state its bus drivers. if a transceiver is required to buffer the 8088 local bus, signals dt/r and den are pro- vided by the 8088. a write cycle also begins with the assertion of ale and the emission of the address. the io/m signal is again asserted to indicate a memory or i/o write operation. in t2, immediately following the address emission, the processor emits the data to be written into the addressed location. this data remains valid until at least the middle of t4. during t2, t3, and tw, the processor asserts the write control signal. the write (wr ) signal becomes active at the begin- ning of t2, as opposed to the read, which is delayed somewhat into t2 to provide time for the bus to float. 13
8088 the basic difference between the interrupt acknowl- edge cycle and a read cycle is that the interrupt ac- knowledge (inta ) signal is asserted in place of the read (rd ) signal and the address bus is floated. (see figure 9) in the second of two successive inta cycles, a byte of information is read from the data bus, as supplied by the interrupt system logic (i.e. 8259a priority interrupt controller). this byte identi- fies the source (type) of the interrupt. it is multiplied by four and used as a pointer into the interrupt vec- tor lookup table, as described earlier. bus timingemedium complexity systems (see figure 10) for medium complexity systems, the mn/mx pin is connected to gnd and the 8288 bus controller is added to the system, as well as a latch for latching the system address, and a transceiver to allow for bus loading greater than the 8088 is capable of han- dling. signals ale, den , and dt/r are generated by the 8288 instead of the processor in this configu- ration, although their timing remains relatively the same. the 8088 status outputs (s2 ,s1 , and s0 ) pro- vide type of cycle information and become 8288 in- puts. this bus cycle information specifies read (code, data, or i/o), write (data or i/o), interrupt ac- knowledge, or software halt. the 8288 thus issues control signals specifying memory read or write, i/o read or write, or interrupt acknowledge. the 8288 provides two types of write strobes, normal and ad- vanced, to be applied as required. the normal write strobes have data valid at the leading edge of write. the advanced write strobes have the same timing as read strobes, and hence, data is not valid at the leading edge of write. the transceiver receives the usual t and oe inputs from the 8288's dt/r and den outputs. the pointer into the interrupt vector table, which is passed during the second inta cycle, can derive from an 8259a located on either the local bus or the system bus. if the master 8289a priority interrupt controller is positioned on the local bus, a ttl gate is required to disable the transceiver when reading from the master 8259a during the interrupt acknowl- edge sequence and software ``poll''. the 8088 compared to the 8086 the 8088 cpu is an 8-bit processor designed around the 8086 internal structure. most internal functions of the 8088 are identical to the equivalent 8086 functions. the 8088 handles the external bus the same way the 8086 does with the distinction of handling only 8 bits at a time. sixteen-bit operands are fetched or written in two consecutive bus cycles. both processors will appear identical to the software engineer, with the exception of execution time. the internal register structure is identical and all instruc- tions have the same end result. the differences be- tween the 8088 and 8086 are outlined below. the engineer who is unfamiliar with the 8086 is referred to the iapx 86, 88 user's manual, chapters 2 and 4, for function description and instruction set informa- tion. internally, there are three differences between the 8088 and the 8086. all changes are related to the 8-bit bus interface. # the queue length is 4 bytes in the 8088, whereas the 8086 queue contains 6 bytes, or three words. the queue was shortened to prevent overuse of the bus by the biu when prefetching instructions. this was required because of the additional time necessary to fetch instructions 8 bits at a time. # to further optimize the queue, the prefetching al- gorithm was changed. the 8088 biu will fetch a new instruction to load into the queue each time there i s a 1 byte hole (space available) in the queue. the 8086 waits until a 2-byte space is available. # the internal execution time of the instruction set is affected by the 8-bit interface. all 16-bit fetches and writes from/to memory take an additional four clock cycles. the cpu is also limited by the speed of instruction fetches. this latter problem only occurs when a series of simple operations occur. when the more sophisticated instructions of the 8088 are being used, the queue has time to fill and the execution proceeds as fast as the exe- cution unit will allow. the 8088 and 8086 are completely software com- patible by virtue of their identical execution units. software that is system dependent may not be com- pletely transferable, but software that is not system dependent will operate equally as well on an 8088 and an 8086. the hardware interface of the 8088 contains the ma- jor differences between the two cpus. the pin as- signments are nearly identical, however, with the fol- lowing functional changes: # a8 a15ethese pins are only address outputs on the 8088. these address lines are latched in- ternally and remain valid throughout a bus cycle in a manner similar to the 8085 upper address lines. # bhe has no meaning on the 8088 and has been eliminated. 14
8088 # sso provides the so status information in the minimum mode. this output occurs on pin 34 in minimum mode only. dt/r , io/m , and sso pro- vide the complete bus status in minimum mode. # io/m has been inverted to be compatible with the mcs-85 bus structure. # ale is delayed by one clock cycle in the mini- mum mode when entering halt, to allow the status to be latched with ale. 231456 10 figure 10. medium complexity system timing 15
8088 absolute maximum ratings * ambient temperature under bias 0 cto a 70 c case temperature (plastic) 0 cto a 95 c case temperature (cerdip) 0 cto a 75 c storage temperature b 65 cto a 150 c voltage on any pin with respect to ground b 1.0 to a 7v power dissipation 2.5 watt notice: this is a production data sheet. the specifi- cations are subject to change without notice. * warning: stressing the device beyond the ``absolute maximum ratings'' may cause permanent damage. these are stress ratings only. operation beyond the ``operating conditions'' is not recommended and ex- tended exposure beyond the ``operating conditions'' may affect device reliability. d.c. characteristics (t a e 0 cto70 c, t case (plastic) e 0 cto95 c, t case (cerdip) e 0 cto75 c, t a e 0 cto55 c and t case e 0 cto75 c for p8088-2 only t a is guaranteed as long as t case is not exceeded) (v cc e 5v g 10% for 8088, v cc e 5v g 5% for 8088-2 and extended temperature express) symbol parameter min max units test conditions v il input low voltage b 0.5 a 0.8 v (note 1) v ih input high voltage 2.0 v cc a 0.5 v (notes 1, 2) v ol output low voltage 0.45 v i ol e 2.0 ma v oh output high voltage 2.4 v i oh eb 400 m a i cc 8088 340 ma t a e 25 c power supply current: 8088-2 350 p8088 250 i li input leakage current g 10 m a0v s v in s v cc (note 3) i lo output and i/o leakage current g 10 m a 0.45v s v out s v cc v cl clock input low voltage b 0.5 a 0.6 v v ch clock input high voltage 3.9 v cc a 1.0 v c in capacitance if input buffer 15 pf fc e 1 mhz (all input except ad 0 ad 7 , rq/gt) c io capacitance of i/o buffer 15 pf fc e 1 mhz ad 0 ad 7 , rq/gt) notes: 1. v il tested with mn/mx pin e 0v v ih tested with mn/mx pin e 5v mn/mx pin is a strap pin 2. not applicable to rq /gt0 and rq /gt1 pins (pins 30 and 31) 3. hold and hlda i li min e 30 m a, max e 500 m a 16
8088 a.c. characteristics (t a e 0 cto70 c, t case (plastic) e 0 cto95 c, t case (cerdip) e 0 cto75 c, t a e 0 cto55 c and t case e 0 cto80 c for p8088-2 only t a is guaranteed as long as t case is not exceeded) (v cc e 5v g 10% for 8088, v cc e 5v g 5% for 8088-2 and extended temperature express) minimum complexity system timing requirements symbol parameter 8088 8088-2 units test min max min max conditions tclcl clk cycle period 200 500 125 500 ns tclch clk low time 118 68 ns tchcl clk high time 69 44 ns tch1ch2 clk rise time 10 10 ns from 1.0v to 3.5v tcl2cl2 clk fall time 10 10 ns from 3.5v to 1.0v tdvcl data in setup time 30 20 ns tcldx data in hold time 10 10 ns tr1vcl rdy setup time into 8284 35 35 ns (notes 1, 2) tclr1x rdy hold time into 8284 0 0 ns (notes 1, 2) tryhch ready setup time 118 68 ns into 8088 tchryx ready hold time 30 20 ns into 8088 trylcl ready inactive to clk b 8 b 8ns (note 3) thvch hold setup time 35 20 ns tinvch intr, nmi, test setup time 30 15 ns (note 2) tilih input rise time (except clk) 20 20 ns from 0.8v to 2.0v tihil input fall time (except clk) 12 12 ns from 2.0v to 0.8v 17
8088 a.c. characteristics (continued) timing responses symbol parameter 8088 8088-2 units test min max min max conditions tclav address valid delay 10 110 10 60 ns tclax address hold time 10 10 ns tclaz address float delay tclax 80 tclax 50 ns tlhll ale width tclch b 20 tclch b 10 ns tcllh ale active delay 80 50 ns tchll ale inactive delay 85 55 ns tllax address hold time to tchcl b 10 tchcl b 10 ns ale inactive tcldv data valid delay 10 110 10 60 ns tchdx data hold time 10 10 ns twhdx data hold time after wr tclch b 30 tclch b 30 ns tcvctv control active delay 1 10 110 10 70 ns tchctv control active delay 2 10 110 10 60 ns tcvctx control inactive delay 10 110 10 70 ns tazrl address float to read 0 0 ns active tclrl rd active delay 10 165 10 100 ns tclrh rd inactive delay 10 150 10 80 ns trhav rd inactive to next tclcl b 45 tclcl b 40 ns address active tclhav hlda valid delay 10 160 10 100 ns trlrh rd width 2tclcl b 75 2tclcl b 50 ns twlwh wr width 2tclcl b 60 2tclcl b 40 ns taval address valid to ale low tclch b 60 tclch b 40 ns toloh output rise time 20 20 ns from 0.8v to 2.0v tohol output fall time 12 12 ns from 2.0v to 0.8v notes: 1. signal at 8284a shown for reference only. see 8284a data sheet for the most recent specifications. 2. set up requirement for asynchronous signal only to guarantee recognition at next clk. 3. applies only to t2 state (8 ns into t3 state). 18
8088 a.c. testing input, output waveform 231456 11 a.c. testing; inputs are driven at 2.4v for a logic ``1'' and 0.45v for a logic ``0''. timing measurements are made at 1.5v for both a logic ``1'' and logic ``0''. a.c. testing load circuit 231456 12 c l includes jig capacitance waveforms bus timingeminimum mode system 231456 13 19
8088 waveforms (continued) bus timingeminimum mode system (continued) 231456 14 notes: 1. all signals switch between v oh and v ol unless otherwise specified. 2. rdy is sampled near the end of t 2 ,t 3 ,t w to determine if t w machines states are to be inserted. 3. two inta cycles run back-to-back. the 8088 local addr/data bus is floating during both inta cycles. control signals are shown for the second inta cycle. 4. signals at 8284 are shown for reference only. 5. all timing measurements are made at 1.5v unless otherwise noted. 20
8088 a.c. characteristics max mode system (using 8288 bus controller) timing requirements symbol parameter 8088 8088-2 units test min max min max conditions tclcl clk cycle period 200 500 125 500 ns tclch clk low time 118 68 ns tchcl clk high time 69 44 ns tch1ch2 clk rise time 10 10 ns from 1.0v to 3.5v tcl2cl1 clk fall time 10 10 ns from 3.5v to 1.0v tdvcl data in setup time 30 20 ns tcldx data in hold time 10 10 ns tr1vcl rdy setup time into 8284 35 35 ns (notes 1, 2) tclr1x rdy hold time into 8284 0 0 ns (notes 1, 2) tryhch ready setup time into 8088 118 68 ns tchryx ready hold time into 8088 30 20 ns trylcl ready inactive to clk b 8 b 8ns (note 4) tinvch setup time for recognition 30 15 ns (intr, nmi, test) (note 2) tgvch rq/gt setup time 30 15 ns tchgx rq hold time into 8088 40 30 ns tilih input rise time (except clk) 20 20 ns from 0.8v to 2.0v tihil input fall time (except clk) 12 12 ns from 2.0v to 0.8v 21
8088 a.c. characteristics (continued) timing responses symbol parameter 8088 8088-2 units test min max min max conditions tclml command active delay 10 35 10 35 ns (note 1) tclmh command inactive delay 10 35 10 35 ns (note 1) tryhsh ready active to 110 65 ns status passive (note 3) tchsv status active delay 10 110 10 60 ns tclsh status inactive delay 10 130 10 70 ns tclav address valid delay 10 110 10 60 ns tclax address hold time 10 10 ns tclaz address float delay tclax 80 tclax 50 ns tsvlh status valid to ale high 15 15 ns (note 1) tsvmch status valid to mce high 15 15 ns (note 1) tcllh clk low to ale valid 15 15 ns (note 1) tclmch clk low to mce (note 1) 15 15 ns tchll ale inactive delay (note 1) 15 15 ns tclmcl mce inactive delay (note 1) 15 15 ns tcldv data valid delay 10 110 10 60 ns tchdx data hold time 10 10 ns c l e 20 100 pf for tcvnv control active delay 5 45 5 45 ns all 8088 outputs (note 1) in addition to tcvnx control inactive delay 10 45 10 45 ns internal loads (note 1) tazrl address float to 0 0 ns read active tclrl rd active delay 10 165 10 100 ns tclrh rd inactive delay 10 150 10 80 ns trhav rd inactive to next tclcl b 45 tclcl b 40 ns address active tchdtl direction control 50 50 ns active delay (note 1) tchdth direction control 30 30 ns inactive delay (note 1) tclgl gt active delay 85 50 ns tclgh gt inactive delay 85 50 ns trlrh rd width 2tclcl b 75 2tclcl b 50 ns toloh output rise time 20 20 ns from 0.8v to 2.0v tohol output fall time 12 12 ns from 2.0v to 0.8v notes: 1. signal at 8284 or 8288 shown for reference only. 2. setup requirement for asynchronous signal only to guarantee recognition at next clk. 3. applies only to t3 and wait states. 4. applies only to t2 state (8 ns into t3 state). 22
8088 a.c. testing input, output waveform 231456 11 a.c. testing; inputs are driven at 2.4v for a logic ``1'' and 0.45v for a logic ``0''. timing measurements are made at 1.5v for both a logic ``1'' and logic ``0''. a.c. testing load circuit 231456 12 c l includes jig capacitance waveforms (continued) bus timingemaximum mode system 231456 15 23
8088 waveforms (continued) bus timingemaximum mode system (using 8288) notes: 231456 16 1. all signals switch between v oh and v ol unless otherwise specified. 2. rdy is sampled near the end of t 2 ,t 3 ,t w to determine if t w machines states are to be inserted. 3. cascade address is valid between first and second inta cycles. 4. two inta cycles run back-to-back. the 8088 local addr/data bus is floating during both inta cycles. control for pointer address is shown for second inta cycle. 5. signals at 8284 or 8288 are shown for reference only. 6. the issuance of the 8288 command and control signals (mrdc , mwtc , amwc , iorc , iowc , aiowc , inta and den) lags the active high 8288 cen. 7. all timing measurements are made at 1.5v unless otherwise noted. 8. status inactive in state just prior to t 4 . 24
8088 waveforms (continued) asynchronous signal recognition note: 231456 17 1. setup requirements for asynchronous signals only to guarantee recognition at next clk. bus lock signal timing (maximum mode only) 231456 18 request/grant sequence timing (maximum mode only) note: 231456 19 1. the coprocessor may not drive the busses outside the region shown without risking contention. hold/hold acknowledge timing (minimum mode only) 231456 20 25
8088 8086/8088 instruction set summary mnemonic and instruction code description data transfer mov e move: 76543210 76543210 76543210 76543210 register/memory to/from register 100010dw mod reg r/m immediate to register/memory 1100011w mod000r/m data data if w e 1 immediate to register 1011wreg data data if w e 1 memory to accumulator 1010000w addr-low addr-high accumulator to memory 1010001w addr-low addr-high register/memory to segment register 10001110 mod0regr/m segment register to register/memory 10001100 mod0regr/m push e push: register/memory 11111111 mod110r/m register 01010reg segment register 000reg110 pop e pop: register/memory 10001111 mod000r/m register 01011reg segment register 000reg111 xchg e exchange: register/memory with register 1000011w modregr/m register with accumulator 10010reg in e input from: fixed port 1110010w port variable port 1110110w out e output to: fixed port 1110011w port variable port 1110111w xlat e translate byte to al 11010111 lea e load ea to register 10001101 modregr/m lds e load pointer to ds 11000101 modregr/m les e load pointer to es 11000100 modregr/m lahf e load ah with flags 10011111 sahf e store ah into flags 10011110 pushf e push flags 10011100 popf e pop flags 10011101 26
8088 8086/8088 instruction set summary (continued) mnemonic and instruction code description arithmetic 76543210 76543210 76543210 76543210 add e add: reg./memory with register to either 000000dw modregr/m immediate to register/memory 100000sw mod000r/m data data if s:w e 01 immediate to accumulator 0000010w data data if w e 1 adc e add with carry: reg./memory with register to either 000100dw modregr/m immediate to register/memory 100000sw mod010r/m data data if s:w e 01 immediate to accumulator 0001010w data data if w e 1 inc e increment: register/memory 1111111w mod000r/m register 01000reg aaa e ascii adjust for add 00110111 baa e decimal adjust for add 00100111 sub e subtract: reg./memory and register to either 001010dw modregr/m immediate from register/memory 100000sw mod101r/m data data if s:w e 01 immediate from accumulator 0010110w data data if w e 1 ssb e subtract with borrow reg./memory and register to either 000110dw modregr/m immediate from register/memory 100000sw mod011r/m data data if s:w e 01 immediate from accumulator 000111w data data if w e 1 dec e decrement: register/memory 1111111w mod001r/m register 01001 reg neg e change sign 1111011w mod011 r/m cmp e compare: register/memory and register 001110dw modregr/m immediate with register/memory 100000sw mod111r/m data data if s:w e 01 immediate with accumulator 0011110w data data if w e 1 aas e ascii adjust for subtract 00111111 das e decimal adjust for subtract 00101111 mul e multiply (unsigned) 1111011w mod100r/m imul e integer multiply (signed) 1111011w mod101r/m aam e ascii adjust for multiply 11010100 00001010 div e divide (unsigned) 1111011w mod110r/m idiv e integer divide (signed) 1111011w mod111r/m aad e ascii adjust for divide 11010101 00001010 cbw e convert byte to word 10011000 cwd e convert word to double word 10011001 27
8088 8086/8088 instruction set summary (continued) mnemonic and instruction code description logic 76543210 76543210 76543210 76543210 not e invert 1111011w mod010r/m shl/sal e shift logical/arithmetic left 110100vw mod100r/m shr e shift logical right 110100vw mod101r/m sar e shift arithmetic right 110100vw mod111r/m rol e rotate left 110100vw mod000r/m ror e rotate right 110100vw mod001r/m rcl e rotate through carry flag left 110100vw mod010r/m rcr e rotate through carry right 110100vw mod011r/m and e and: reg./memory and register to either 001000dw modregr/m immediate to register/memory 1000000w mod100r/m data data if w e 1 immediate to accumulator 0010010w data data if w e 1 test e and function to flags. no result: register/memory and register 1000010w modregr/m immediate data and register/memory 1111011w mod000r/m data data if w e 1 immediate data and accumulator 1010100w data data if w e 1 or e or: reg./memory and register to either 000010dw modregr/m immediate to register/memory 1000000w mod001r/m data data if w e 1 immediate to accumulator 0000110w data data if w e 1 xor e exclusive or: reg./memory and register to either 001100dw modregr/m immediate to register/memory 1000000w mod110r/m data data if w e 1 immediate to accumulator 0011010w data data if w e 1 string manipulation rep e repeat 1111001z movs e move byte/word 1010010w cmps e compare byte/word 1010011w scas e scan byte/word 1010111w lods e load byte/wd to al/ax 1010110w stos e stor byte/wd from al/a 1010101w control transfer call e call: direct within segment 11101000 disp-low disp-high indirect within segment 11111111 mod010r/m direct intersegment 10011010 offset-low offset-high seg-low seg-high indirect intersegment 11111111 mod011r/m 28
8088 8086/8088 instruction set summary (continued) mnemonic and instruction code description jmp e unconditional jump: 76543210 76543210 76543210 direct within segment 11101001 disp-low disp-high direct within segment-short 11101011 disp indirect within segment 11111111 mod100r/m direct intersegment 11101010 offset-low offset-high seg-low seg-high indirect intersegment 11111111 mod101r/m ret e return from call: within segment 11000011 within seg adding immed to sp 11000010 data-low data-high intersegment 11001011 intersegment adding immediate to sp 11001010 data-low data-high je/jz e jump on equal/zero 01110100 disp jl/jnge e jump on less/not greater 01111100 disp or equal jle/jng e jump on less or equal/ 01111110 disp not greater jb/jnae e jump on below/not above 01110010 disp or equal jbe/jna e jump on below or equal/ 01110110 disp not above jp/jpe e jump on parity/parity even 01111010 disp jo e jump on overflow 01110000 disp js e jump on sign 01111000 disp jne/jnz e jump on not equal/not zero 01110101 disp jnl/jge e jump on not less/greater 01111101 disp or equal jnle/jg e jump on not less or equal/ 01111111 disp greater jnb/jae e jump on not below/above 01110011 disp or equal jnbe/ja e jump on not below or 01110111 disp equal/above jnp/jpo e jump on not par/par odd 01111011 disp jno e jump on not overflow 01110001 disp jns e jump on not sign 01111001 disp loop e loop cx times 11100010 disp loopz/loope e loop while zero/equal 11100001 disp loopnz/loopne e loop while not 11100000 disp zero/equal jcxz e jump on cx zero 11100011 disp int e interrupt type specified 11001101 type type 3 11001100 into e interrupt on overflow 11001110 iret e interrupt return 11001111 29
8088 8086/8088 instruction set summary (continued) mnemonic and instruction code description 76543210 76543210 processor control clc e clear carry 11111000 cmc e complement carry 11110101 stc e set carry 11111001 cld e clear direction 11111100 std e set direction 11111101 cli e clear interrupt 11111010 sti e set interrupt 11111011 hlt e halt 11110100 wait e wait 10011011 esc e escape (to external device) 11011xxx modxxxr/m lock e bus lock prefix 11110000 notes: al e 8-bit accumulator ax e 16-bit accumulator cx e count register ds e data segment es e extra segment above/below refers to unsigned value greater e more positive: less e less positive (more negative) signed values if d e 1 then ``to'' reg; if d e 0 then ``from'' reg if w e 1 then word instruction; if w e 0 then byte instruction if mod e 11 then r/m is treated as a reg field if mod e 00 then disp e 0 * , disp-low and disp-high are absent if mod e 01 then disp e disp-low sign-extended to 16 bits, disp-high is absent if mod e 10 then disp e disp-high; disp-low if r/m e 000 then ea e (bx) a (si) a disp if r/m e 001 then ea e (bx) a (di) a disp if r/m e 010 then ea e (bp) a (si) a disp if r/m e 011 then ea e (bp) a (di) a disp if r/m e 100 then ea e (si) a disp if r/m e 101 then ea e (di) a disp if r/m e 110 then ea e (bp) a disp * if r/m e 111 then ea e (bx) a disp disp follows 2nd byte of instruction (before data if re- quired) * except if mod e 00 and r/m e then ea e disp-high: disp-low. if s:w e 01 then 16 bits of immediate data form the oper- and if s:w e 11 then an immediate data byte is sign extended to form the 16-bit operand if v e 0 then ``count'' e 1; if v e 1 then ``count'' in (cl) register x e don't care z is used for string primitives for comparison with zf flag segment override prefix 001reg110 reg is assigned according to the following table: 16-bit (w e 1) 8-bit (w e 0) segment 000 ax 000 al 00 es 001 cx 001 cl 01 cs 010 dx 010 dl 10 ss 011 bx 011 bl 11 ds 100 sp 100 ah 101 bp 101 ch 110 si 110 dh 111 di 111 bh instructions which reference the flag register file as a 16-bit object use the symbol flags to represent the file: flags e x:x:x:x:(of):(df):(if):(tf):(sf):(zf):x:(af):x:(pf):x:(cf) mnemonics ? intel, 1978 data sheet revision review the following list represents key differences be- tween this and the -005 data sheet. please review this summary carefully. 1. the intel 8088 implementation technology (hmos) has been changed to (hmos-ii). 30

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