Jim wrote: > > I need to find a source for EPROM's for a Williams Defender main PCB. I have > a couple of PCB's missing the ROM's. > > The number on the EPROM is #7641. It may be a Harris chip and may actually > be a BPROM. I will be burning these chips from my original ROM's > > Any help would be greatly appreciated > > Jim I have the blank Harris 7641 proms for $10 each or $15 programmed. The 75S474 is a suitable substitute, but about the same price & as hard to find. -- Big Bear Thanks The Real Bob Roberts™ For parts http://personal.msy.bellsouth.net/~bob147 Williams 7641 Decoder Roms - Replacements, Pinouts and Programming ------------------------------------------------------------------ Revision B - Compiled and Entered by Tim Foley The Video Decoder roms used in Defender (and other Williams Games) are 7641 24 pin Proms. Since I have yet to even find one of these little devils, I've been searching for a substitute. National Semiconductor makes two Proms that are fully pin compatible with the 7641, the 74S474 and the 74S475. The main difference between the two is access times and more importantly, the 474 is a tri-state output whereas the 475 is an open collector. In short...use the 474 for reliability. The 74S474 has more varieties available. 7641 (512 x 8) 4096-Bit Prom .----------. A7 --| 1 24|-- Vcc A6 --| 2 23|-- A8 A5 --| 3 22|-- ??? (Tied to Vcc on Defender CPU Board) A4 --| 4 21|-- CS1 (NOT, active low) A3 --| 5 20|-- CS2 (NOT, active low) A2 --| 6 19|-- CE3 A1 --| 7 18|-- CE4 A0 --| 8 17|-- D7 D0 --| 9 16|-- D6 D1 --| 10 15|-- D5 D2 --| 11 14|-- D4 GND--| 12 13|-- D3 .----------. National Semiconductor 74S474 (512 x 8) 4096-Bit TTL PROM .----------. Pin Names A7 --| 1 24|-- Vcc ---------------------------- A6 --| 2 23|-- A8 A0-A8 Addresses A5 --| 3 22|-- NC G1,G2,G3,G4 Output Enables A4 --| 4 21|-- G1 (NOT) GND Ground A3 --| 5 20|-- G2 (NOT) NC No Connection A2 --| 6 19|-- G3 Q0-Q7 Outputs A1 --| 7 18|-- G4 Vcc Power Supply A0 --| 8 17|-- Q7 Q0 --| 9 16|-- Q6 Q1 --| 10 15|-- Q5 Q2 --| 11 14|-- Q4 GND--| 12 13|-- Q3 .----------. Notes: 1) Also same as 74S475. 74S472 & 74S473 are 20 Pins not 24 pins like the 7641. 2) Vcc is 4.75vdc to 5.25vdc for Commerical grade. 3) 74S475 has Open Collector Outputs 4) 74S474 has Tri-State Outputs. PROM Programming Procedure -------------------------- National's Proms use titanium-tungsten (Ti:W) fuse links designed to program efficiently with only 10.5V applied. The Proms are shipped from the factory with all fuses intact, as a result, the outputs will be low (logical "0") for all addresses. To generate high (logical "1") levels at the outputs, the device must be programmed. Information regarding commercially available programming equipment may be obtained from National. If it is desired to build your own programmer, the following conditions must be observered: 1. Programming should be attempted only at ambient temperatures between 15 degress celcius and 30 degrees celcius. 2. Address and Enable inputs must be driven with TTL logic levels during programming and verification. 3. Programming will occur at the selected address when Vcc is at 10.5v, and at the selected bit location when the output pin representing that bit, is at 10.5v, and the device is subsequently enabled. To achieve these conditions in the appropiate sequence, the following procedure must be followed: a) Select the desired word by applying high or low levels to the appropriate address inputs. Disable the device by applying a high level to one or more of the "active low" chip enable inputs. b) Increase Vcc from nominal to 10.5v (+/- 0.5v) with a slew rate between 1.0 and 10.0 V/us. Since Vcc is the source of the current required to program the fuse as well as the Icc for the device at the programming voltage, it must be capable of supply 750 mA at 11.0v. c) Select the output where a logical high is desired by raising that output voltage to 10.5v (+/- 0.5v). Limit the slew rate from 1.0 to 10.0 V/us. This voltage change may occur simultaneously with the increase in Vcc, but must not precede it. It is critical that only the one output at a time be programmed since the internal circuits can only supply programming current to one bit at a time. Ouputs not being programmed must be left open or connected to a high impedance source of over 20k minimum. (Remember that the outputs of the device are disabled at this time). d) Enable the device by taking the chip enable(s) to a low level. This is done with a pulse of 10us. The 10us duration refers to the time that the circuit (device) is enabled. Normal input levels are used and rise and fall times are not critical. e) Verify that the bit has been programmed by first removing the programming voltage from the output and then reducing Vcc to 4.0v (+/- 0.2V) for one verification and to 6.0v (+/- 0.2v) for a second verification. Verification at Vcc levels of 4.0v and 6.0v will guarantee proper output states over the Vcc and temperature range of the prom. The device must be enabled to sense the state of the outputs. During verification, the loading of the output must be within specified Iol and Ioh limits. Steps b,c and d must be repeated up to 10 times or until verification that the bit has been programmed. f) Following verification, apply five additional programming pulses to the bit being programmed. The programming procedure is now complete for the selected bit. g) Repeat steps a through f for each bit to eb programmed to a high level. If the procedure is performed on a automatic programmer, the duty cycle of Vcc at the programming voltage must be limited to a maximum of 25%. This is necessary to minimize device junction temperatures. After all selected bits are programmed, the entire contents of the memory should be verified. Note: Since only an enabled device is programmed, it is possible to program these parts at the board level if all programming parameters are complied with. ---------------------------------------------------------------------------------- Tim Foley - timf@interlog.com Williams Defender Web Page: http://www.interlog.com/~timf/defender_page/defender.htm ---------------------------------------------------------------------------------- *** Some of this information was obtained from the National Semiconductor Memory Databook, 400067, 1990 Edition. ** Thanks to Roger Boots for pointing out the difference between the 474 and 475 (Unless you like 'fuses' ... ;)