74903 prom contents for 4FDC?

[kyeakel]

I'm trying to resurrect a 4FDC, it currently does nothing. I have checked power, and tested all chips on the board with the exception of the UART and 1771. I have been trying to make sense of the data contained in the 74903 (IC23) it does not seem like it's correct. I have a Dataman 48pro2 programmer that I used to read the contents. I have looked thru Marcus database that I downloaded around July 2020, but did not see any files containing the data.

Hoping someone here has read a known good one?

Thanks,

Kipp

[Roger Hanscom]

I don't own a 4FDC, Kipp, but the 16FDC has the same PROM with the 74903 Cromemco part number.  It's a TBP18S030.  Just guessing, but maybe it's the same part?

Roger

[Steven Feinsmith]

No, the data in the PROM between different controllers may be programmed differently as it is a PROM.

Steven

On Fri, Apr 12, 2024 at 5:54 PM Roger Hanscom <norwe...@gmail.com> wrote:

I don't own a 4FDC, Kipp, but the 16FDC has the same PROM with the 74903 Cromemco part number.  It's a TBP18S030.  Just guessing, but maybe it's the same part?

Roger

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[Mike Stein]

FWIW, looks like the 74903 is also used in the 16FDC (IC36).

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[kyeakel]

I will look and see if I have a 16FDC, my 74903 chip is actually a 74S288. 

Thanks,

Kipp

[Aron Hoekstra]

I have a working 4FDC. My IC23 is a TI-branded 74903. I am not sure how to read the contents of it, though. I have a TL866II-Plus but I'm not sure if it supports that chip type. To complicate matters, that chip at one point suffered a broken pin leg and I have a bodge wire solution in place right now. I would have to get a good substitute leg soldered on there in order to get the contents read.

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[Walt Perko]

Hi,

 

I was looking at my 16FDC …

 

CromemCo Part: 74903 = DM29751 = ? 74S288N = AM27S19PC = 256bit PROM 

 

 

 

 

 

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[Amardeep Chana]

I haven't checked the 4FDC circuit diagram, but very likely that PROM is part of the data separator circuit.  The 1771 application notes don't have the PROM contents shown, but the 179x notes do.  Page 12 of the following document.

http://www.bitsavers.org/components/westernDigital/FD179X_Application_Notes_Jun1980.pdf

Since the same Cromemco part number is used for the 16FDC PROM, the contents are likely just the vendor supplied table values.  At the very least you can check to see if they match what you have.

Regards,

Amardeep

[Mike Arnold]

Hi Kipp,

Just had a quick look at the circuit diagram and I am pretty sure that the PROM is an address decoder for the UART. The circuitry for the 16FDC is pretty much the same around the 5501 so I guess that the 74903 PROMs are interchangeable.

I have a 4FDC in my box of boards so I could pull the chip and post it to you (on loan) as I do not have a PROM programmer to read it (and too lazy to design one). However, I am away on holiday until 1st May. If you have not had any joy by the time I return, get in touch.

Good luck.

Mike

[Walt Perko]

Hi,

 

I went through the TL866II-Plus list of chips, there is nothing on the list for any of the part numbers; 

 

CromemCo Part No.74903 = DM29751 = 74S288N = AM27S19PC = 256bit PROM

 

 

 

 

 

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From: crom...@googlegroups.com On Behalf Of Aron Hoekstra
Sent: Friday, April 12, 2024 5:33 PM
To: crom...@googlegroups.com
Subject: Re: 74903 prom contents for 4FDC?

 

I have a working 4FDC. My IC23 is a TI-branded 74903. I am not sure how to read the contents of it, though. I have a TL866II-Plus but I'm not sure if it supports that chip type. To complicate matters, that chip at one point suffered a broken pin leg and I have a bodge wire solution in place right now. I would have to get a good substitute leg soldered on there in order to get the contents read.

To view this discussion on the web visit https://groups.google.com/d/msgid/cromemco/CAD9iBD%2BReJ1%3DoNr5kkS%2Bu5eRzDVCUav784ed-b2rWTEHt0t_yw%40mail.gmail.com.

[kyeakel]

Turns out I did have a 16FDC, and the contents of the 74903 on that board matches what is on the 74903 from my 4FDC. Thanks for the suggestion to look at the 16FDC. I'm including a screen shot of the data burned into one of these if anyone needs it in future.

Thanks!

Kipp

[Roger Hanscom]

Thanks for lending some sanity to this discussion, Mike:

>> Just had a quick look at the circuit diagram and I am pretty sure that the PROM is an address decoder for the UART.

>> The circuitry for the 16FDC is pretty much the same around the 5501 so I guess that the 74903 PROMs are interchangeable.

A look at the 16FDC schematic will verify that the PROM is used to translate the lower address bits (and sWO) from the bus to address the TI UART.  It makes no sense whatsoever that Cromemco would use the same part number (74903) to reference two different parts.  Due to the simple nature of the PROM, it is quite possible that they used different PROMs for 74903's, however.  All the ones I've looked at are TBP18S030N from T.I.

Roger

[Steven Feinsmith]

I understand that you have a PROM chip that was used on Cromemco 4FDC. This chip was a once-programmed chip that could read the code like ROM. To ensure that you hook up the PROM correctly and read the code, it would be best to have a datasheet. I believe that PROM is used on both 4FDC and 16FDC because they have the same part number, but their programming codes are different configurations based on hardware. However, I came across someone who said that using the TI866II device was a mistake. It would ruin the PROM quickly because it was not configured correctly. You should never use the TI866 (any version), which belongs in the trash can because it is a piece of junk. I had a horrible experience with the TI866II when I tried to read my old PROM chip, which I no longer use for experimental purposes. I carefully configured it to read the chip, but the device quickly ruined it. The same incident happened with the second PROM chip, which ended up ruined. I threw away the TI866II a long time ago and used my professional devices, which could read anything without risking damage to the chip. It is important to keep in mind that the 4FDC has some kind of problem, but it was corrected when they released the 16FDC board or later. I strongly encourage you to rework with the 4FDC but use the same PROM and see if the board is working. If so, then it is best to leave it alone. Please let me know if you have any questions or if there's anything else I can help you with.

Steven

On Fri, Apr 12, 2024 at 4:49 PM kyeakel <kye...@atlanticbb.net> wrote:

--

[Steven Feinsmith]

Rich Camarda did a great job! The PROMs for 4FDC and 16FDC differ at address 0014. It is advisable to rely on something other than chip-stamped numbers since PROMs are usually programmed to control hardware at a lower level.

However, obtaining blank PROMs might be challenging as vendors stopped to make them a long time ago. Furthermore, replacing the original PROM requires a suitable programmer.

Steven

On Fri, Apr 12, 2024 at 4:49 PM kyeakel <kye...@atlanticbb.net> wrote:

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[Jazzman]

In addition to the previously listed cross-references for the 74S288, a MMI 6331 or 63S081, Harris 7603 or IM5610 should work. You can usually find blank PROMs at arcade chip suppliers. An older programmer like the Data I/O 29B with a Unipak 2B can program them.

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[Mike Stein]

I'd sure be surprised if there are any Cromemco PROMs with the same Cromemco part number but different contents as Steven suggests (unless the relevant locations are never read); that would cause even more confusion than Cromemco's unfortunate choice of 74xxx as the part number prefix for their PROMs.

Most IC manufacturers of the day made PROMs and I assume like any other chip Cromemco just used whatever was available and best priced; most of the ones I've seen were the TBP18S030N or the 74s188 and in my experience they were mostly used as address decoders.

As to reading them, I never had a problem reading them as a 2716 with an adapter to reroute the pins; I had to read a few when we were discussing the different PROMs in the 256KZ to accommodate different memory models. 

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[Mike Stein]

Programming PROMs is quite different from programming EPROMs, and very few (cheap) programmers could do both.

To view this discussion on the web visit https://groups.google.com/d/msgid/cromemco/008401da8d95%246ea1c530%244be54f90%24%40brainless.org.

[David Roberts]

There was a magazine project many years ago that described the construction of a PROM programmer for these types of devices.

It used switches and LEDs, and was a manual programmer. 32 bytes is not that difficult (or time consuming) to program a byte at a time.

Incidentally, the devices are still available. I bought 200 off of four device types (800 total) last year for work. These devices were amongst them. However, they are not cheap... Because these were for work, they have provenance back to the manufacturer...

By the rules of the game, a part number should be unique from a supplier (including the programmed contents).

Dave

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[Walt Perko]

Hi,

 

I was thinking that IF there is a difference in the 4FDC and the 16FDC PROMs that perhaps somebody swapped out the original 4FDC part with a 16FDC part. 

 

I tried looking at photos of 4FDC boards on eBay, but none of them seem to have a part label 74903 on them. 

 

 

 

 

==============================================================================================
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http://www.R2Pv1.com/  RoboGuts™ Intelligent content for 3D printing making S.T.E.A.M. education better, easier and more affordable 

 

Experiments to learn how to use various Electronic Components, Structured Computer Programming, Phonemes for Speech &Song in any language, and Art.

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==============================================================================================

            Sent from the Cyber7

 

 

From: crom...@googlegroups.com On Behalf Of Mike Stein
Sent: Sunday, April 14, 2024 7:56 AM
To: crom...@googlegroups.com
Subject: Re: 74903 prom contents for 4FDC?

 

I'd sure be surprised if there are any Cromemco PROMs with the same Cromemco part number but different contents as Steven suggests (unless the relevant locations are never read); that would cause even more confusion than Cromemco's unfortunate choice of 74xxx as the part number prefix for their PROMs.

To view this discussion on the web visit https://groups.google.com/d/msgid/cromemco/CAHHfo1vHTgduK48hy%3DadTx0hNX6kSMSDN4h%2B1U3ffhxvHzHFMw%40mail.gmail.com.

[kyeakel]

Here are my findings with this board. 

1) On the schematic U31 - 2708 ROM the outputs are labeled incorrectly D0 - D7 are swapped. This just caused confusion to me, the board is correct.

2) U23 pin 9 switches U49 A-B. This swaps D6 + D7 with D3 + D4 at the output of the data bus. Mine never selects B, so the ROM contents cannot be read properly making it impossible to boot RDOS 1.1. The inputs to the 74903 seem correct to me.

I'm including the schematic for reference.

3) I'm guessing I have bad 74903 chips on both my 4fdc and 16fdc, doesn't seem likely to me but what else could it be?

4) Steven: You posted, "Rich Camarda did a great job! The PROMs for 4FDC and 16FDC differ at address 0014." I didn't see the chip data in your post. Where did you get this info?

Thanks,

Kipp 

[Mike Arnold]

Kipp, do you get an RDOS prompt? I guess not based on your original post. 

In order to get a prompt a whole lot of things have to be working correctly (eg RAM, 5501, RS232 drivers/receivers). Have you tried to set the non-auto baud rate switch? I think it forces it to 300 baud and will allow you to see if RDOS sends out the welcome message upon reset. Once you have that you can start to worry about disk access. Just a thought...

Mike

[David Roberts]

Over on VCFED I developed the test code for a "Hello Dave" 2708 EPROM. 

Once we got this working with a 4FDC, we migrated to a "stripped down" RDOS with no frills.

I should still have the code somewhere if that would help?

Dave

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[Steven Feinsmith]

Two different patterns, 4FDC and 16FDC, showed different data under address 0014. 4FDC displayed "EE," while 16FDC displayed "6E."

For many years, I noticed people focused on IC stamped, which meant it was compatible on different boards, which meant they were the same. This did not apply to ROM/PROM/EPROM/E2PROM and others because the data are programmed to control the hardware. There are even the same issues with PAL and others.

Steven

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[Steven Feinsmith]

I reviewed the 4FDC board diagram, which can be found at the following URL: http://www.s100computers.com/Hardware%20Manuals/Cromemco/Cromemco%204FDC%20Manual.pdf. According to the diagram, socket IC18 contains 74903, even though the part number displayed is IC23.

The 16FDC board has two PROMs, 74903 and 74918B. Unfortunately, the image from S100computers.com was not clear enough.

Best regards,

Steven

To view this discussion on the web visit https://groups.google.com/d/msgid/cromemco/008c01da8e86%24825373c0%2486fa5b40%24%40brainless.org.

[Walt Perko]

Hi,

 

Okay, here’s a higher resolution and straight on photo of the CromemCo 16FDC board; 

 

To view this discussion on the web visit https://groups.google.com/d/msgid/cromemco/CAGJMgmVKqTL4BxAfqk8HtOPfzSfCXCGiNBWamcShCC%3Dhv0ELtw%40mail.gmail.com.

[Steven Feinsmith]

I have saved the following text as requested:

The 16FDC has IC36 and IC37, which are PROM chips, 74903 and 74918B. The picture was clear enough, but it needs to be compared with the 4FDC. Cromemco modified the newer version with different IC numbers. I believe the 4FDC had only one PROM installed.

I verified that 4FDC and 16FDC's 74903 had different data despite having the same IC labels. If I recall correctly, during the old days with Cromemco, 4FDC was more prone to issues. The manufacturer discontinued and replaced it with the newer 16FDC and 64FDC.

Steven

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[Rich Camarda]

Trying again to send the pics. I used a STAG ZM2000 Programmer to read the proms.

Rich

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[kyeakel]

Thanks Rich! 

It looks like my chip matches your 16fdc chip, and not the 4fdc chip. (locations 04, and 14 are different between the 4fdc and 16fdc).

Mike, 

     I don't get any RDOS prompt, as the RDOS code is never executed.

David,

    For debugging I have the ZPU, a John Monahan RAM/ROM card, and the 4fdc. I have the ROM on john's card at E000 and have my NO_RAM monitor chip located there. The ZPU boots to E000. With this monitor I can see the 4fdc rom at C000, but the data is incorrect as read by the ZPU. I have traced the issue back to the 74903 chip on the 4fdc. Now to find a substitute for the 74288 rom chip...

Kipp

[kyeakel]

I have now created a truth table of the 4fdc 74903 rom, and it shows that my ROM is correct. The difference between my ROM and Rich's is the clearing of 2 lines on the serial / parallel interface of the board. (pins 1 and 4). On a read of the Uart external inputs my ROM sets /ISTB low, and on a write to the output port, my ROM sets /OSTB low. I'm including a spreadsheet of my truth table. Comments welcome..

Kipp