1. introduction. the communication standard ieee 1284 was created to supply the need for an existing defined standard for bi-directional parallel communication between the pc and printing peripherals. being backward compatible with the old specification parallel centronics, this standard offers more functionality and performance for new pc and peripheral products. 74act1284 is designed to be compliant with both the ieee1284 and parallel centronics standards. 2. device description. 74act1284 can be used in epp, ecp and byte modes. - the ecp (extended capabilities port) mode provides an asynchronous, bi-directional, parallel peripheral interface for personal computers. - the epp (enhanced parallel port) mode allows high-speed transfers in either direction. this mode is ideal for real-time-controlled peripherals, such as network adapters, data acquisition and other devices. - the byte mode allows the transfer of data in the reverse direction if the data lines are bi-directional. these devices allow data transmission in the a-to-b direction or b- to-a direction, depending on the logic level of the direction-control pin (dir). figure 1: pin layout the output drive mode is determinated by the high-drive control pin (hd). hd enables the outputs b to switch from open collector to totem pole. the a side outputs have totem-pole outputs only. table 1 shows the pin outs and function of this device: b1 b2 b3 b4 v cc v cc b5 b6 b7 hd a1 a2 a3 a4 gnd gnd a5 a6 a7 dir 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 february 2002 1/6 AN1524 application note 74act1284 standard logic: a high speed ieee 1284 tranceiver m. porto
AN1524 - application note 2/6 table 1: pin outs and functions the features and benefits of i eee 1284 std are summarized in the table below. table 2: features and benefits of ieee 1284 standard the device is designed with 300mv of hysteresis in order to filter input noise and to prevent false commutation when a slow input edge is applied to the input. figure 2: static thresholds typical value pin number symbol name & function 11 hd high drive enable inputs 10 dir direction control inputs 1 - 4 a1 - a4 side a inputs or outputs 17 - 20 b4 - b1 side b inputs and outputs 7 - 9 a5 - a7 side a input 12 - 14 b7 - b5 side b output 15 - 16 v cc power supply 5 - 6 gnd ground features benefits 5v 10% v cc ttl-compatible inputs flow-through architecture optimizes printed circuit board layout center pin v cc and gnd configuration minimizes high speed switching noise a to b and b to a transmission for bits 1, 2, 3 and 4 configurable data flow 14ma b port output currents guarenteed 350mv minimum hysteresis fastest device on the market maximum tpd 6.5ns @ v cc = 4.5v so and tssop packaging 0.00 1.00 2.00 3.00 4.00 5.00 6.00 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 vin (v) vout (v) a side input limit vih=2v max temp=+85c vil=0.8v max temp=-40c temp=25c v cc =5.0v vih=1.60v vil=1.06v
AN1524 - application note 3/6 3. output impedance measurement technique. for these measurements we have to prepare the testing bench as seen in the following figure. figure 3: output impedance testing bench by means of waveform generator a sine wave signal is applied, with amplitude of 1vpp and frequency of 100khz in order to avoid parasitic jig capacitances that could affect the measurement accuracy. then the generator is connected to circuit made by a 47 m f capacitor, that uncouples the dc voltage between the generator and the d.u.t., and a 200 w trimmer is used as a voltage divider in combination with the d.u.t. output impedance. figure 4:output impedance block diagram when d.u.t. r i 5 0 w vi + c1 = 47mf r1 = 200w r1 ro vin vout ar vout vin ro ro r 1 + --------------------- - = (1) ro vout r vin vout C --------------------------- vout vin ------------ r vin vin -------- - vout vin ----------- - C --------------------------- xr 1 x C ------------- === (2) x vout vin ----------- - =
AN1524 - application note 4/6 when we inject a signal on point a and we measure the transfer characteristic over r1, (r as output), the following comparison is in force: we can measure a / r => out of formula (3) we can calculate x => by filling in x in formula (2), we find ro. if we look at these calculations we see that we only need a certain resistance value for r1. if we know this resistance, we only need to measure a / r and then make the calculation. we do these measurements in function with the following parameters: - supply voltage: 4.5v - 5.5v - temperature: 25c - 45c - batch: almost impossible using this measurement technique, the st1284 output impedance measures at 27 w (typ). 4. application information. before ieee 1284 std, there was no defined electrical specification for the driver, receiver, termination, and capacitance requirements that require compatibility between devices. host adapters and peripherals were built with different pull-up values on the control lines, open-collectors or open-drain, and totem-pole drivers for the data and control lines. frequently 10nf capacitors were used on the data and strobe lines. a typical application circuit before ieee1284 std is show below. figure 5: a typical application circuit before ieee 1284 std a r --- 20 vout vin ----------- - log 20 x log == (3) slct pe busy ack 33 w slin init error 33 w 33 w afd stb 1k w db25 pro-ieee std 1284 parallel-port host solution pd (7.0) c
AN1524 - application note 5/6 the next figure shows the same application using the ieee 1284 std device figure 6: a typical application circuit using the ieee 1284 std 5. conclusion. this report gives a brief description on stmicroelectronics std i eee1284 device, which offers superior performance when compared with competition. furthermore, this report was designed to help choose the correct bus interface device in std ieee1284 applications. 5 status sn74act1284 a1 Ca4 b1 C b4 4 data 4 data a5, a6 or a7 b5, b6, or b7 2 control 2 control to peripheral via ieee std 1284 connector and cable to super i / o sn74act1284 a1 C a4 b1 C b4 4 data 4 data a5, a6 or a7 b5, b6, or b7 2 control 2 control ieee std 1284 host solution using two sn74act1284 devices
AN1524 - application note 6/6 information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specification mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectronics. the st logo is a registered trademark of stmicroelectronics ? 2002 stmicroelectronics - printed in italy - all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - finland - france - germany - hong kong - india - isreal - italy - japan - malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - u.s.a. http://www.st.com
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