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CY7C4255 CY7C4265
8K/16K x 18 Deep Sync FIFOs
Features
* High-speed, low-power, first-in first-out (FIFO) memories * 8K x 18 (CY7C4255) * 16K x 18 (CY7C4265) * 0.5 micron CMOS for optimum speed/power * High-speed 100-MHz operation (10-ns read/write cycle times) * Low power -- ICC = 45 mA * Fully asynchronous and simultaneous read and write operation * Empty, Full, Half Full, and programmable Almost Empty and Almost Full status flags * TTL compatible * Retransmit function * Output Enable (OE) pins * Independent read and write enable pins * Center power and ground pins for reduced noise * Supports free-running 50% duty cycle clock inputs * Width Expansion Capability * Depth Expansion Capability * 64-pin TQFP and 64-pin STQFP * Pin-compatible density upgrade to CY7C42X5 family * Pin-compatible density upgrade to IDT72205/15/25/35/45 are 18 bits wide and are pin/functionally compatible to the CY7C42X5 Synchronous FIFO family. The CY7C4255/65 can be cascaded to increase FIFO depth. Programmable features include Almost Full/Almost Empty flags. These FIFOs provide solutions for a wide variety of data buffering needs, including high-speed data acquisition, multiprocessor interfaces, and communications buffering. These FIFOs have 18-bit input and output ports that are controlled by separate clock and enable signals. The input port is controlled by a Free-Running Clock (WCLK) and a Write Enable pin (WEN). When WEN is asserted, data is written into the FIFO on the rising edge of the WCLK signal. While WEN is held active, data is continually written into the FIFO on each cycle. The output port is controlled in a similar manner by a free-running Read Clock (RCLK) and a Read Enable pin (REN). In addition, the CY7C4255/65 have an Output Enable pin (OE). The read and write clocks may be tied together for single-clock operation or the two clocks may be run independently for asynchronous read/write applications. Clock frequencies up to 100 MHz are achievable. Retransmit and Synchronous Almost Full/Almost Empty flag features are available on these devices. Depth expansion is possible using the Cascade Input (WXI, RXI), Cascade Output (WXO, RXO), and First Load (FL) pins. The WXO and RXO pins are connected to the WXI and RXI pins of the next device, and the WXO and RXO pins of the last device should be connected to the WXI and RXI pins of the first device. The FL pin of the first device is tied to VSS and the FL pin of all the remaining devices should be tied to VCC.
Functional Description
The CY7C4255/65 are high-speed, low-power, first-in first-out (FIFO) memories with clocked read and write interfaces. All
Logic Block Diagram
D0 - 17
INPUT REGISTER
WCLK
WEN
WRITE CONTROL
FLAG PROGRAM REGISTER
RAM ARRAY 8K x 18 16K x 18 WRITE POINTER
FLAG LOGIC
FF EF PAE PAF SMODE
READ POINTER
RS
RESET LOGIC
FL/RT WXI WXO/HF RXI RXO
EXPANSION LOGIC
THREE-STATE OUTPUT REGISTER OE
READ CONTROL 4255-1
Q0 - 17
RCLK
REN
Cypress Semiconductor Corporation Document #: 38-06004 Rev. *B
*
3901 North First Street
*
San Jose
*
CA 95134 * 408-943-2600 Revised August 11, 2004
CY7C4255 CY7C4265
Pin Configurations
REN LD OE RS VCC GND EF Q17 Q16 GND Q15 VCC/SMODE
TQFP/STQFP Top View
64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49
D16 D17 GND RCLK
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
CY7C4255 CY7C4265
48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33
Q14 Q13 GND Q12 Q11 VCC Q10 Q9 GND Q8 Q7 Q6 Q5 GND Q4 VCC
4255-3 FL/RT WCLK WEN WXI VCC PAF RXI FF WXO/HF RXO PAE Q0 Q1 GND Q2 Q3
Functional Description (continued)
The CY7C4255/65 provides five status pins. These pins are decoded to determine one of five states: Empty, Almost Empty, Half Full, Almost Full, and Full. The Half Full flag shares the WXO pin. This flag is valid in the stand-alone and width-expansion configurations. In the depth expansion, this pin provides the expansion out (WXO) information that is used to signal the next FIFO when it will be activated.
The Empty and Full flags are synchronous, i.e., they change state relative to either the Read Clock (RCLK) or the Write Clock (WCLK). When entering or exiting the Empty states, the flag is updated exclusively by the RCLK. The flag denoting Full states is updated exclusively by WCLK. The synchronous flag architecture guarantees that the flags will remain valid from one clock cycle to the next. The Almost Empty/Almost Full flags become synchronous if the VCC/SMODE is tied to VSS. All configurations are fabricated using an advanced 0.5 CMOS technology. Input ESD protection is greater than 2001V, and latch-up is prevented by the use of guard rings.
Selection Guide
7C4255/65-10 Maximum Frequency (MHz) Maximum Access Time (ns) Minimum Cycle Time (ns) Minimum Data or Enable Set-Up (ns) Minimum Data or Enable Hold (ns) Maximum Flag Delay (ns) Active Power Supply Current (ICC1) (mA) Commercial Industrial 100 8 10 3 0.5 8 45 50 CY7C4265 16K x18 7C4255/65-15 66.7 10 15 4 1 10 45 50 7C4255/65-25 40 15 25 6 1 15 45 50 7C4255/65-35 28.6 20 35 7 2 20 45 50
CY7C4255 Density Package 8K x 18
64-pin TQFP, STQFP 64-pin TQFP, STQFP
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Signal Name D0 -17 Q0-17 WEN REN WCLK Description Data Inputs Data Outputs Write Enable Read Enable Write Clock I/O I O I I I Data inputs for an 18-bit bus. Data outputs for an 18-bit bus. Enables the WCLK inpu.t Enables the RCLK input. The rising edge clocks data into the FIFO when WEN is LOW and the FIFO is not Full. When LD is asserted, WCLK writes data into the programmable flag-offset register. The rising edge clocks data out of the FIFO when REN is LOW and the FIFO is not Empty. When LD is asserted, RCLK reads data out of the programmable flag-offset register. Dual-Mode Pin: Single device or width expansion - Half Full status flag. Cascaded - Write Expansion Out signal, connected to WXI of next device. When EF is LOW, the FIFO is empty. EF is synchronized to RCLK. When FF is LOW, the FIFO is full. FF is synchronized to WCLK. When PAE is LOW, the FIFO is almost empty based on the almost-empty offset value programmed into the FIFO. PAE is asynchronous when VCC/SMODE is tied to VCC; it is synchronized to RCLK when VCC/SMODE is tied to VSS. When PAF is LOW, the FIFO is almost full based on the almost full offset value programmed into the FIFO. PAF is asynchronous when V CC/SMODE is tied to VCC; it is synchronized to WCLK when VCC/SMODE is tied to VSS. When LD is LOW, D0-17 (Q0-17) are written (read) into (from) the programmable-flag-offset register. Dual-Mode Pin: Cascaded - The first device in the daisy chain will have FL tied to VSS; all other devices will have FL tied to VCC. In standard mode or width expansion, FL is tied to VSS on all devices. Not Cascaded - Tied to VSS. Retransmit function is also available in stand-alone mode by strobing RT. Cascaded - Connected to WXO of previous device. Not Cascaded - Tied to VSS. Cascaded - Connected to RXO of previous device. Not Cascaded - Tied to VSS. Cascaded - Connected to RXI of next device. Resets device to empty condition. A reset is required before an initial read or write operation after power-up. When OE is LOW, the FIFO's data outputs drive the bus to which they are connected. If OE is HIGH, the FIFO's outputs are in High Z (high-impedance) state. Dual-Mode Pin: Asynchronous Almost Empty/Almost Full flags - tied to VCC. Synchronous Almost Empty/Almost Full flags - tied to VSS. (Almost Empty synchronized to RCLK, Almost Full synchronized to WCLK.) Function
RCLK
Read Clock
I
WXO/HF
Write Expansion Out/Half Full Flag Empty Flag Full Flag Programmable Almost Empty Programmable Almost Full Load First Load/ Retransmit
O
EF FF PAE
O O O
PAF
O
LD FL/RT
I I
WXI RXI RXO RS OE VCC/SMODE
Write Expansion Input Read Expansion Input Read Expansion Output Reset Output Enable Synchronous Almost Empty/ Almost Full Flags
I I O I I I
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Maximum Ratings [1]
(Above which the useful life may be impaired. For user guidelines, not tested.) Storage Temperature ................................ -65C to +150C Ambient Temperature with Power Applied . -55C to +125C Supply Voltage to Ground Potential ............... -0.5V to +7.0V DC Voltage Applied to Outputs in High Z State ............................................... -0.5V to +7.0V DC Input Voltage ..........................................-0.5V to VCC+0.5V Range Commercial Industrial[3] Output Current into Outputs (LOW)............................. 20 mA Static Discharge Voltage............................................ >2001V (per MIL-STD-883, Method 3015) Latch-Up Current..................................................... >200 mA
Operating Range[2]
Ambient Temperature 0C to +70C -40C to +85C VCC 5V 10% 5V 10%
Electrical Characteristics Over the Operating Range[3]
7C42X5-10 Parameter VOH VOL VIH[4] VIL[5] IIX IOZL IOZH ICC1[6] ICC2
[7]
7C42X5-15 Min. 2.4 Max.
7C42X5-25 Min. 2.4 Max.
7C42X5- 35 Min. 2.4 Max. Unit V 0.4 2.0 -0.5 -10 -10 VCC 0.8 +10 +10 45 50 10 15 V V V A A mA mA mA mA
Description Output HIGH Voltage Output LOW Voltage Input HIGH Voltage Input LOW Voltage Input Leakage Current Output OFF, High Z Current Active Power Supply Current Average Standby Current
Test Conditions VCC = Min., IOH = -2.0 mA VCC = Min., IOL = 8.0 mA
Min. 2.4
Max.
0.4 2.0 -0.5 VCC 0.8 +10 +10 45 50 10 15 2.0 -0.5 -10 -10
0.4 VCC 0.8 +10 +10 45 50 10 15 2.0 -0.5 -10 -10
0.4 VCC 0.8 +10 +10 45 50 10 15
VCC = Max. OE > VIH, VSS < VO < VCC Com'l Ind Com'l Ind
-10 -10
Capacitance[8, 9]
Parameter CIN COUT Description Input Capacitance Output Capacitance Test Conditions TA = 25C, f = 1 MHz, VCC = 5.0V Max. 5 7 Unit pF pF
Notes: 1. The Voltage on any input or I/O pin cannot exceed the power pin during power-up. 2. TA is the "Instant On" case temperature. 3. See the last page of this specification for Group A subgroup testing information. 4. The VIH and V IL specifications apply for all inputs except WXI, RXI. The WXI, RXI pin is not a TTL input. It is connected to either RXO, WXO of the previous device or V SS. 5. The VIH and V IL specifications apply for all inputs except WXI, RXI. The WXI, RXI pin is not a TTL input. It is connected to either RXO, WXO of the previous device or V SS. 6. Input signals switch from 0V to 3V with a rise/fall time of less than 3 ns, clocks and clock enables switch at 20 MHz, while data inputs switch at 10 MHz. Outputs are unloaded. ICC1(typical) = (25 mA+(freq -20 MHz)*(1.0 mA/MHz)). 7. All inputs = VCC - 0.2V, except RCLK and WCLK (which are switching at frequency = 20 MHz), and FL/RT which is at Vss. All outputs are unloaded. 8. Tested initially and after any design changes that may affect these parameters. 9. Tested initially and after any process changes that may affect these parameters.
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
AC Test Loads and Waveforms[10, 11]
R1 1.1 K 5V OUTPUT CL INCLUDING JIG AND SCOPE R2 680
4255-4
ALL INPUT PULSES
3.0V GND 3 ns 90% 10% 90% 10% 3 ns
4255-5
Equivalent to:
THEVENIN EQUIVALENT 410 OUTPUT
1.91V
Switching Characteristics Over the Operating Range
7C42X5-10 Parameter tS tA tCLK tCLKH tCLKL tDS tDH tENS tENH tRS tRSR tRSF tPRT tRTR tOLZ tOE tOHZ tWFF tREF tPAFasynch Description Clock Cycle Frequency Data Access Time Clock Cycle Time Clock HIGH Time Clock LOW Time Data Set-Up Time Data Hold Time Enable Set-Up Time Enable Hold Time Reset Pulse Width[12] Reset Recovery Time Reset to Flag and Output Time Retransmit Pulse Width Retransmit Recovery Time Output Enable to Output in Low Z[12] Output Enable to Output Valid Output Enable to Output in High Z[13] Write Clock to Full Flag Read Clock to Empty Flag Clock to Programmable Almost-Full (Asynchronous mode, VCC/SMODE tied to VCC) Flag[13] 30 60 0 3 3 7 7 8 8 12 2 10 4.5 4.5 3 0.5 3 0.5 10 8 10 35 65 0 3 3 8 8 10 10 16 Min. Max. 100 8 2 15 6 6 4 1 4 1 15 10 15 45 75 0 3 3 12 12 15 15 20 7C42X5-15 Min. Max. 66.7 10 2 25 10 10 6 1 6 1 25 15 25 55 85 0 3 3 15 15 20 20 25 7C42X5-25 Min. Max. 40 15 2 35 14 14 7 2 7 2 35 20 35 7C42X5-35 Min. Max. 28.6 20 Unit MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
tPAFsynch tPAEasynch tPAEsynch tHF
Clock to Programmable Almost-Full Flag (Synchronous mode, VCC/SMODE tied to VSS) Clock to Programmable Almost-Empty Flag[14] (Asynchronous mode, VCC/SMODE tied to VCC) Clock to Programmable Almost-Full Flag (Synchronous mode, VCC/SMODE tied to VSS) Clock to Half-Full Flag
8 12 8 12
10 16 10 16
15 20 15 20
20 25 20 25
ns ns ns ns
Notes: 10. CL = 30 pF for all AC parameters except for tOHZ. 11. CL = 5 pF for tOHZ. 12. Pulse widths less than minimum values are not allowed. 13. Values guaranteed by design, not currently tested. 14. tPAFasynch, tPAEasynch, after program register write will not be valid until 5 ns + tPAF(E).
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Characteristics Over the Operating Range (continued)
7C42X5-10 Parameter tXO tXI tXIS tSKEW1 tSKEW2 tSKEW3 Description Clock to Expansion Out Expansion in Pulse Width Expansion in Set-Up Time Skew Time between Read Clock and Write Clock for Full Flag Skew Time between Read Clock and Write Clock for Empty Flag Skew Time between Read Clock and Write Clock for Programmable Almost Empty and Programmable Almost Full Flags (Synchronous Mode only) 4.5 4 5 5 10 Min. Max. 6 6.5 5 6 6 15 7C42X5-15 Min. Max. 10 10 10 10 10 18 7C42X5-25 Min. Max. 15 14 15 12 12 20 7C42X5-35 Min. Max. 20 Unit ns ns ns ns ns ns
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms
Write Cycle Timing
tCLK tCLKH WCLK tDS D0 -D17 tENS WEN tWFF FF tSKEW1 [15] RCLK tWFF tENH
NO OPERATION
tCLKL
tDH
REN
4255-6
Read Cycle Timing
tCLK tCLKH RCLK tENS REN tREF EF tA Q0 -Q17 tOLZ tOE OE
[16] tSKEW2
VALID DATA
tCLKL
tENH
NO OPERATION
tREF
tOHZ
WCLK
WEN
4255-7
Notes: 15. tSKEW1 is the minimum time between a rising RCLK edge and a rising WCLK edge to guarantee that FF will go HIGH during the current clock cycle. If the time between the rising edge of RCLK and the rising edge of WCLK is less than tSKEW1, then FF may not change state until the next WCLK rising edge. 16. tSKEW2 is the minimum time between a rising WCLK edge and a rising RCLK edge to guarantee that EF will go HIGH during the current clock cycle. It the time between the rising edge of WCLK and the rising edge of RCLK is less than tSKEW2, then EF may not change state until the next RCLK rising edge.
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Reset Timing [17]
tRS RS tRSR REN, WEN, LD tRSF EF,PAE tRSF FF,PAF, HF tRSF Q0 - Q17 OE=0
4255-8
OE=1
[18]
First Data Word Latency after Reset with Simultaneous Read and Write
WCLK tDS D0 -D17 tENS WEN tSKEW2 RCLK tREF EF tFRL
[19]
D0 (FIRSTVALID WRITE)
D1
D2
D3
D4
REN tA Q0 -Q17 tOLZ tOE OE
4255-9
tA D0
[19]
D1
Notes: 17. The clocks (RCLK, WCLK) can be free-running during reset. 18. After reset, the outputs will be LOW if OE = 0 and three-state if OE = 1. 19. When tSKEW2 > minimum specification, tFRL (maximum) = tCLK + tSKEW2. When tSKEW2 < minimum specification, tFRL (maximum) = either 2*tCLK + tSKEW2 or tCLK + tSKEW2. The Latency Timing applies only at the Empty Boundary (EF = LOW). 20. The first word is available the cycle after EF goes HIGH, always.
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Empty Flag Timing
WCLK tDS D0 -D17 tENS WEN tFRL[18] RCLK tSKEW2 EF tREF tREF tSKEW2 tREF tFRL[18] D0 tENH tENS tDS D1 tENH
REN
OE tA Q0 -Q17 D0
4255-10
Full FlagTiming
NO WRITE WCLK tSKEW1 D0 -D17 tWFF FF
[15]
NO WRITE
tDS
tSKEW1 [15] DATA WRITE tWFF tWFF
DATA WRITE
WEN
RCLK tENH tENS REN tENS tENH
OE
LOW tA tA DATA READ NEXT DATA READ
4255-11
Q0 -Q17
DATA IN OUTPUT REGISTER
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Half-Full Flag Timing
tCLKH WCLK tENS tENH WEN tHF HF HALF FULL OR LESS HALF FULL + 1 OR MORE tHF RCLK tENS REN
4255-12
tCLKL
HALF FULLOR LESS
Programmable Almost Empty Flag Timing
tCLKH WCLK tENS tENH WEN tPAE PAE [20] N + 1 WORDS IN FIFO tPAE n WORDS IN FIFO tCLKL
RCLK tENS REN
4255-13
Note: 21. PAE is offset = n. Number of data words into FIFO already = n.
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Programmable Almost Empty Flag Timing (applies only in SMODE (SMODE is LOW))
tCLKH WCLK tENS tENH WEN tCLKL
WEN2 tENS tENH PAE tSKEW3 [23] RCLK tENS REN
4255-14
Note 22 tPAE synch
N + 1 WORDS INFIFO
Note 24
tPAE synch
tENS tENH
Programmable Almost Full Flag Timing
tCLKH Note 25 WCLK tENS tENH WEN tPAF PAF [26] FULL- M WORDS INFIFO [27] tPAF RCLK tENS REN
4255-15
tCLKL
FULL- (M+1) WORDS IN FIFO [28]
Notes: 22. PAE offset - n. 23. tSKEW3 is the minimum time between a rising WCLK and a rising RCLK edge for PAE to change state during that clock cycle. If the time between the edge of WCLK and the rising RCLK is less than tSKEW3, then PAE may not change state until the next RCLK. 24. If a read is preformed on this rising edge of the read clock, there will be Empty + (n-1) words in the FIFO when PAE goes LOW. 25. PAF offset = m. Number of data words written into FIFO already = 8192 - (m + 1) for the CY7C4255 and 16384 - (m + 1) for the CY7C4265. 26. PAF is offset = m. 27. 8192 - m words in CY7C4255 and 16384 - m words in CY7C4265. 28. 8192 - (m + 1) words in CY7C4255 and 16384 - (m + 1) CY7C4265.
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Programmable Almost Full Flag Timing (applies only in SMODE (SMODE is LOW))
tCLKH WCLK tENS tENH WEN tCLKL Note 29
Note WEN2 tENS tENH PAF FULL- M + 1 WORDS IN FIFO
30
tPAF FULL- M WORDS IN FIFO [27] tSKEW3[31] tPAF synch
RCLK tENS REN
4255-16
tENS tENH
Write Programmable Registers
tCLK tCLKH WCLK tENS LD tENS WEN tDS D0 -D17 PAE OFFSET PAF OFFSET D0 - D11
4255-17
tCLKL
tENH
tDH
PAE OFFSET
Notes: 29. If a write is performed on this rising edge of the write clock, there will be Full - (m-1) words of the FIFO when PAF goes LOW. 30. PAF offset = m. 31. tSKEW3 is the minimum time between a rising RCLK and a rising WCLK edge for PAF to change state during that clock cycle. If the time between the edge of RCLK and the rising edge of WCLK is less than tSKEW3, then PAF may not change state until the next WCLK rising edge.
Document #: 38-06004 Rev. *B
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CY7C4255 CY7C4265
Switching Waveforms (continued)
Read Programmable Registers
tCLK tCLKH RCLK tENS LD tENS WEN tA Q0 -Q17 UNKNOWN PAE OFFSET PAF OFFSET PAE OFFSET
4255-18
tCLKL
tENH
Write Expansion Out Timing
tCLKH WCLK Note 31 tXO WXO tENS WEN
4255-19
Note 32
tXO
Read Expansion Out Timing
tCLKH WCLK Note 33 tXO RXO tENS REN
4255-20
tXO
Write Expansion In Timing
tXI WXI
WCLK
tXIS
4255-21
Notes: 32. Write to Last Physical Location. 33. Read from Last Physical Location.
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Switching Waveforms (continued)
Read Expansion In Timing
tXI RXI tXIS
4255-22
RCLK
Retransmit Timing
FL/RT
[34, 35, 36]
tPRT tRTR REN/WEN
EF/FF and all async flags HF/PAE/PAF
Notes: 34. Clocks are free-running in this case. 35. The flags may change state during Retransmit as a result of the offset of the read and write pointers, but flags will be valid at tRTR. 36. For the synchronous PAE and PAF flags (SMODE), an appropriate clock cycle is necessary after tRTR to update these flags.
4255-23
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CY7C4255 CY7C4265
Architecture
The CY7C4256/65 consists of an array of 8K/16K words of 18 bits each (implemented by a dual-port array of SRAM cells), a read pointer, a write pointer, control signals (RCLK, WCLK, REN, WEN, RS), and flags (EF, PAE, HF, PAF, FF). The CY7C4255/65 also includes the control signals WXI, RXI, WXO, RXO for depth expansion. operation. When the LD pin is set LOW, and WEN is LOW, the next offset register in sequence is written. The contents of the offset registers can be read on the output lines when the LD pin is set LOW and REN is set LOW; then, data can be read on the LOW-to-HIGH transition of the Read Clock (RCLK). Table 1. Write Offset Register LD 0 WEN 0 WCLK[37] Selection Writing to offset registers: Empty Offset Full Offset No Operation Write Into FIFO No Operation
Resetting the FIFO
Upon power-up, the FIFO must be reset with a Reset (RS) cycle. This causes the FIFO to enter the Empty condition signified by EF being LOW. All data outputs go LOW after the falling edge of RS only if OE is asserted. In order for the FIFO to reset to its default state, a falling edge must occur on RS and the user must not read or write while RS is LOW.
0 1 1
1 0 1
FIFO Operation
When the WEN signal is active (LOW), data present on the D0 - 17 pins is written into the FIFO on each rising edge of the WCLK signal. Similarly, when the REN signal is active LOW, data in the FIFO memory will be presented on the Q0-17 outputs. New data will be presented on each rising edge of RCLK while REN is active LOW and OE is LOW. REN must set up tENS before RCLK for it to be a valid read function. WEN must occur tENS before WCLK for it to be a valid write function. An output enable (OE) pin is provided to three-state the Q0-17 outputs when OE is deasserted. When OE is enabled (LOW), data in the output register will be available to the Q0-17 outputs after tOE. If devices are cascaded, the OE function will only output data on the FIFO that is read enabled. The FIFO contains overflow circuitry to disallow additional writes when the FIFO is full, and under flow circuitry to disallow additional reads when the FIFO is empty. An empty FIFO maintains the data of the last valid read on its Q0-17 outputs even after additional reads occur.
Flag Operation
The CY7C4255/65 devices provide five flag pins to indicate the condition of the FIFO contents. Empty and Full are synchronous. PAE and PAF are synchronous if VCC/SMODE is tied to VSS. Full Flag The Full Flag (FF) will go LOW when device is Full. Write operations are inhibited whenever FF is LOW regardless of the state of WEN. FF is synchronized to WCLK, i.e., it is exclusively updated by each rising edge of WCLK. Empty Flag The Empty Flag (EF) will go LOW when the device is empty. Read operations are inhibited whenever EF is LOW, regardless of the state of REN. EF is synchronized to RCLK, i.e., it is exclusively updated by each rising edge of RCLK. Programmable Almost Empty/Almost Full Flag The CY7C4255/65 features programmable Almost Empty and Almost Full Flags. Each flag can be programmed (described in the Programming section) a specific distance from the corresponding boundary flags (Empty or Full). When the FIFO contains the number of words or fewer for which the flags have been programmed, the PAF or PAE will be asserted, signifying that the FIFO is either Almost Full or Almost Empty. See Table 2 for a description of programmable flags. When the SMODE pin is tied LOW, the PAF flag signal transition is caused by the rising edge of the write clock and the PAE flag transition is caused by the rising edge of the read clock.
Programming
The CY7C4255/65 devices contain two 14-bit offset registers. Data present on D0 - 13 during a program write will determine the distance from Empty (Full) that the Almost Empty (Almost Full) flags become active. If the user elects not to program the FIFO's flags, the default offset values are used (see Table 2). When the Load LD pin is set LOW and WEN is set LOW, data on the inputs D0-13 is written into the Empty offset register on the first LOW-to-HIGH transition of the Write Clock (WCLK). When the LD pin and WEN are held LOW then data is written into the Full offset register on the second LOW-to-HIGH transition of the Write Clock (WCLK). The third transition of the Write Clock (WCLK) again writes to the Empty offset register (see Table 1). Writing all offset registers does not have to occur at one time. One or two offset registers can be written and then, by bringing the LD pin HIGH, the FIFO is returned to normal read/write
Notes: 37. The same selection sequence applies to reading from the registers. REN is enabled and read is performed on the LOW-to-HIGH transition of RCLK.
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Retransmit
The retransmit feature is beneficial when transferring packets of data. It enables the receipt of data to be acknowledged by the receiver and retransmitted if necessary. The Retransmit (RT) input is active in the stand-alone and width expansion modes. The retransmit feature is intended for use when a number of writes equal to or less than the depth of the FIFO have occurred and at least one word has been read since the last RS cycle. A HIGH pulse on RT resets the interTable 2. Flag Truth Table Number of Words in FIFO CY7C4255 - 8K x 18 0 1 to n
[38]
nal read pointer to the first physical location of the FIFO. WCLK and RCLK may be free running but must be disabled during and tRTR after the retransmit pulse. With every valid read cycle after retransmit, previously accessed data is read and the read pointer is incremented until it is equal to the write pointer. Flags are governed by the relative locations of the read and write pointers and are updated during a retransmit cycle. Data written to the FIFO after activation of RT are transmitted also. The full depth of the FIFO can be repeatedly retransmitted.
CY7C4265 - 16K x 18 0 1 to n
[38]
FF H H H H H L
PAF H H H H L L
HF H H H L L L
PAE L L H H H H
EF L H H H H H
(n+1) to 4096 4097 to (8192-(m+1)) (8192-m)[39] to 8191 8192
(n+1) to 8192 8193 to (16384 -(m+1)) (16384-m)[39] to 16383 16384
Notes: 38. n = Empty Offset (Default Values: CY7C4255/CY7C4265 n = 127). 39. m = Full Offset (Default Values: CY7C4255/CY7C4265 n = 127).
Document #: 38-06004 Rev. *B
Page 16 of 22
CY7C4255 CY7C4265
Width Expansion Configuration
The CY7C4255/65 can be expanded in width to provide word widths greater than 18 in increments of 18. During width expansion mode all control line inputs are common and all flags are available. Empty (Full) flags should be created by ANDing the Empty (Full) flags of every FIFO; the PAE and PAF flags can be detected from any one device. This technique will avoid reading data from, or writing data to the FIFO that is "staggered" by one clock cycle due to the variations in skew between RCLK and WCLK. Figure 1 demonstrates a 36-word width by using two CY7C4255/65s.
RESET (RS) DATA IN (D) 36
18 18
RESET (RS)
WRITE CLOCK (WCLK) WRITE ENABLE (WEN) LOAD (LD) PROGRAMMABLE(PAE) HALF FULL FLAG (HF) FF FULL FLAG (FF)
18
7C4255 7C4265 7C4255 7C4265
READ CLOCK (RCLK) READ ENABLE (REN) OUTPUT ENABLE (OE) PROGRAMMABLE (PAF)
EMPTY FLAG (EF) EF FF EF
18
DATA OUT (Q)
36
FIRST LOAD (FL) WRITE EXPANSION IN (WXI) READ EXPANSION IN (RXI)
4255-24
Figure 1. Block Diagram of 8K x18/16K x 18 Synchronous FIFO Memory Used in a Width Expansion Configuration
Document #: 38-06004 Rev. *B
Page 17 of 22
CY7C4255 CY7C4265
Depth Expansion Configuration (with Programmable Flags)
The CY7C4255/65 can easily be adapted to applications requiring more than 8192/16384 words of buffering. Figure 2 shows Depth Expansion using three CY7C42X5s. Maximum depth is limited only by signal loading. Follow these steps: 1. The first device must be designated by grounding the First Load (FL) control input. 2. All other devices must have FL in the HIGH state. 3. The Write Expansion Out (WXO) pin of each device must be tied to the Write Expansion In (WXI) pin of the next device. 4. The Read Expansion Out (RXO) pin of each device must be tied to the Read Expansion In (RXI) pin of the next device. 5. All Load (LD) pins are tied together. 6. The Half-Full Flag (HF) is not available in the Depth Expansion Configuration. 7. EF, FF, PAE, and PAF are created with composite flags by ORing together these respective flags for monitoring. The composite PAE and PAF flags are not precise.
WXO RXO 7C4255 7C4265
VCC FL FF EF PAE PAF WXI RXI
WXO RXO
DATA IN(D) VCC
7C4255 7C4265
DATA OUT (Q)
FL FF EF PAF PAE WXI RXI
WRITE CLOCK(WCLK) WRITE ENABLE(WEN) RESET (RS)
WXO RXO 7C4255 7C4265
READ CLOCK(RCLK) READ ENABLE(REN) OUTPUT ENABLE(OE)
LOAD (LD) FF PAF FF EF PAE EF
PAFWXI RXI PAE FIRST LOAD (FL)
4255-25
Figure 2. Block Diagram of 8Kx18/16Kx18 Synchronous FIFO Memory with Programmable Flags used in Depth Expansion Configuration Document #: 38-06004 Rev. *B Page 18 of 22
CY7C4255 CY7C4265
Typical AC and DC Characteristics
NORMALIZED tA vs. SUPPLY VOLTAGE 1.20 NORMALIZED t A NORMALIZED t A 1.10 1.00 0.90 0.80 4.00
NORMALIZED tA vs. AMBIENT TEMPERATURE 1.60 1.40 1.20 1.00 0.80 0.60 -55.00 VCC = 5.0V
TA = 25C
4.50
5.00
5.50
6.00
5.00
65.00
125.00
SUPPLY VOLTAGE (V) NORMALIZED SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.40 NORMALIZED I CC NORMALIZED I CC 1.20 1.00 0.80 0.60 4.00 VIN = 3.0V TA = 25C f = 28 MHz 4.50 5.00 5.50 6.00
AMBIENT TEMPERATURE(C) NORMALIZED SUPPLYCURRENT vs. FREQUENCY 1.75 NORMALIZED I CC 1.50 1.25 1.00 0.75 0.50 20.00 VCC = 5.0V TA = 25C VIN = 3.0V 30.00 40.00 50.00 60.00
NORMALIZED SUPPLY CURRENT vs. AMBIENT TEMPERATURE 1.20 1.10 1.00 0.90 0.80 -55.00 VIN = 3.0V VCC=5.0V f = 28 MHz 5.00 65.00 125.00
SUPPLY VOLTAGE (V)
AMBIENT TEMPERATURE (C)
FREQUENCY (MHz)
Document #: 38-06004 Rev. *B
Page 19 of 22
CY7C4255 CY7C4265
Ordering Information
8Kx18 Deep Sync FIFO Speed (ns) 10 15 Ordering Code CY7C4255-10AC CY7C4255-10ASC CY7C4255-15AC Package Name A65 A64 A65 Package Type 64-Lead Thin Quad Flatpack 64-Lead Small Thin Quad Flatpack 64-Lead Thin Quad Flatpack Commercial Operating Range Commercial
16Kx18 Deep Sync FIFO Speed (ns) 10 Ordering Code CY7C4265-10AC CY7C4265-10ASC CY7C4265-10AI 15 CY7C4265-15AC CY7C4265-15ASC Package Name A65 A64 A65 A65 A64 Package Type 64-Lead Thin Quad Flatpack 64-Lead Small Thin Quad Flatpack 64-Lead Thin Quad Flatpack 64-Lead Thin Quad Flatpack 64-Lead Small Thin Quad Flatpack Industrial Commercial Operating Range Commercial
Package Diagrams
64-Pin Thin Plastic Quad Flat Pack (10 x 10 x 1.4 mm) A64
51-85051-A
Document #: 38-06004 Rev. *B
Page 20 of 22
CY7C4255 CY7C4265
Package Diagrams (continued)
64-Lead Thin Plastic Quad Flat Pack (14 x 14 x 1.4 mm) A65
51-85046-B
Document #: 38-06004 Rev. *B
Page 21 of 22
(c) Cypress Semiconductor Corporation, 2004. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
CY7C4255 CY7C4265
Document Title: CY7C4255, CY7C4265 8K/16K X 18 Deep Sync FIFOs Document Number: 38-06004 REV. ** *A *B ECN NO. 106465 122257 252889 Issue Date 07/11/01 12/26/02 See ECN Orig. of Change SZV RBI YDT Description of Change Change from Spec Number: 38-00468 to 38-06004 Power up requirements added to Maximum Ratings Information Removed PLCC package and pruned parts from Order Information
Document #: 38-06004 Rev. *B
Page 22 of 22

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