Cromemco ZPU Reproduction

[Rich Camarda]

Hi All,

Well, after finally finishing this project which started a while back, but I never had the time to complete, I can say the reproduction board of the Cromemco ZPU is working well.

This is a repro of the Rev F version ZPU (which had the latest fixes as far as I know). I have 2 of these running, and one of them is connected to the IMSAI front panel. It is working in a Cromemco system with Z80 Cromix 11.27, CDOS 2.58, and CP/M 2.2, as well as the IMSAI front panel system which has a CCS 2422, TUART, and RAM 17, running CP/M 2.2.

This board follows the Cromemco "Rev F" schematic and component placement *exactly, and the only exceptions to the original are;

- Layout is for a EzSBC PSU5, or Pololu 24V22F regulator (or equivalent 2.5A +)

- Shorting jumper block for 2 / 4 MHz instead of a switch (in 40 years I never used the "2" position)

- Added a "user defined" LED and resistor (not connected to any signal, and can be configured as user wants, or leave unconnected. I use the IORQ signal)

- Added shorting jumpers for most cut trace options (except the Rev F fix, which I left as a cut trace option for the M1 signal if you decide you don't want that fix)

I have 1 bare board left, and can sell it to someone who can build, and test, in their existing working system (PM me). There would need to be some commitment to build and test it in a reasonable time-frame, so I could then release the files in order to be able to have it available for anyone interested (possibly Todd G. would take over ordering?).

For folks looking to have a classic Z80 CPU board, with Power on Jump, and Front Panel connection, this is a great board to have, and run in it a system, or help when debugging other hardware.

The other two reproductions I have done (CCS 2422, and the Compupro System Support 1) are also working well.

Have a great weekend!

Rich

[Roger Hanscom]

Hi Rich,

Looks like a great board!!  If you have no other takers, I could build one up.  I have Cromemco gear to test it out on (16FDC, 32FDC, 64KZ, 256KZ, etc.), but I have no "front panel" systems.  I am set up to run either CDOS, CP/M 2.2, or Z80 Cromix.  Rev F is a good one to reproduce.  I have had issues with earlier revs. not working in some backplanes.

Roger

[Rich Camarda]

Hi Roger,

OK, sounds good. PM me your info, and I will get it out to you. Would like to hear how it works in your system!

Thanks,

Rich

[Roger Hanscom]

Me again, Rich,

>> OK, sounds good. PM me your info, and I will get it out to you. Would like to hear how it works in your system!

My address is:

Roger Hanscom

3914 Ridge Way

Mount Vernon, WA 98273

I would like it if you would let me reimburse you for the postage costs.  Is that OK?

Roger

[Rich Camarda]

Hi Roger,

Did you get my PM with the tracking #?

Rich

[Roger Hanscom]

I'm rounding up all the components that I'll need to build the ZPU.  Want to be able to build it as quickly as possible without waiting for a parts order to arrive in the mail.  Just a couple of questions:

1.  I don't have much in the way of plain 74 TTL.  Almost all of my supply is 74LS.  Did you find it was a problem using 74LS where 74 was called for?

2.  What is the organization of RN1 and RN2?  Side to side(i.e. 8 resistors)?  I have some 4.7k but they are 1 pin common (i.e. 15 resistors).

That's all ..... for now.  *smile*

Roger

[Roger Hanscom]

>> Did you get my PM with the tracking #?

No.  E-mail addr is norwe...@gmail.com.

Roger

[randy482]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://deramp.com/downloads/mfe_archive/010-S100%2520Computers%2520and%2520Boards/00-Cromemco/10-Cromemco%2520S100%2520Boards/ZPU/Cromemco%2520ZPU%2520Instruction%2520Manual.pdf&ved=2ahUKEwjg8JuEvYP4AhWjmWoFHbvDA6AQFnoECAkQAQ&usg=AOvVaw0sDJzB3ZoZbyawlJQrKZzH

[Rich Camarda]

Ok, sent you an email, let me know if you receive it.

Rich

[MikeS]

For some reason I didn't see a reply to your question: are plain 74 TTL chips required where they are used in the original?

 

m

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[randy482]

Bus drivers should be full power chips (no S, LS, HCT, etc).

Randy

[Roger Hanscom]

>>  Bus drivers should be full power chips (no S, LS, HCT, etc).

I see that on this board 74367's are called for .... lots of them.  I have enough LS367 to build one, but not many 74367 in my cache.  Might have to rob some from socketed ZPU's that I have???

I have a Rev. F1 ZPU that uses 74367s, but unfortunately isn't socketed.  I have another Rev. C card that is socketed and uses 74LS367's.  As I remember, the Rev. C card is finicky about the backplane it is running in.  In a *real* Cromemco backplane it works well, but not so well in some other backplanes.  I haven't done a full inventory of all my ZPUs to see what's what.

Roger

[rcam...@aol.com]

Yes, I decided to go with the original 74367's just to be sure all worked ok. They were only $0.69 at Anchor, or Jameco.

-----Original Message-----
From: Roger Hanscom <norwe...@gmail.com>
To: crom...@googlegroups.com
Sent: Tue, May 31, 2022 5:44 pm
Subject: Re: Cromemco ZPU Reproduction

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.

[Roger Hanscom]

OK, it's been a short while since Rich announced his new version of the ZPU.  I built one, and it works well with CDOS and ITC CP/M 2.2.  I will test it with Z80 Cromix soon .... as soon as I can locate my boot diskettes.  It also works with my S100computers IDE/CF board (sixteen 8 MB "drives" on one CF).  The board is high quality, and went together easily.  I'd recommend it to anybody who has a need for a ZPU.  IMO, Cromemco was the Cadillac of early micros, and most of their gear is built like the proverbial brick outhouse!

The board silkscreen calls for quite a bit of 74 TTL.  I don't have much, so I just used 74LS in almost all cases.  I did have a number of 74367 chips, but not enough to do the entire board (I think there are something like 15(!) required).  So I used some 74LS367 (I tried to put the LS versions of the chips toward the top of the board (away from the S100 connector) assuming that the 74367s that drive the bus would be closer to the bottom of the board.  I didn't bother to make a close examination of the schematic to verify that.)  Also, I used a Z80B, only because it was the first Z80 chip I could find.  I'll test it with a Z80A soon.

Rich tells me that he will release the board to Todd soon, so that it will be available for purchase.

Rich ought to be commended for his efforts in reproducing this great Z80 CPU card.  It must have been a "bear" to capture the original schematic in KiCad!!!  The board is high quality, and the silkscreen is very informative with respect to parts placement, and jumper options.  All-in-all, a great assembly experience!!

Roger

[Rich Camarda]

Thanks Roger, I am glad it is working well for you! 

Yes, these reproductions from old schematics and manuals are a challenge, but rewarding when they work. As an FYI the other 2 boards I have done, are still running solid in my systems.( The CCS 2422, and the Compupro System Support 1 reproductions). I will be turning over the files to Todd soon for the Sys Support 1, and the ZPU (He already has the CCS 2422).

Not sure if I will do another, and I only fit it in when there is time, as it is more of a learning thing for me. Maybe the 256KZ would be another challenge!

Rich

[randy482]

I have been giving thoughts to an updated 256kz board.

The 256kz is strongly tied to Cromix. A newer design is in order:

The 256kz 64k RAM chips are a poor choice, I would recommend going 62256 chips. I would add options to use a CPLD to allow more logic in less space.  Have either jumper options for all Cromix options, and a DRI compatible MMU. This may mean multiple CPLD loads if there isn't space to do all that where jumper selection would set mode.

If there is room for 16 RAM chips (512K) then that would simplify Cromix to get full RAM.

Randy

[Roger Hanscom]

>> The 256kz 64k RAM chips are a poor choice, I would recommend going 62256 chips.

There was an S-100 board that used up to thirty-two 62256 chips.  It came out in the mid-80's.  Called the SRE-1M.  I have a bare board and the documentation for it (including a schematic).  I have no idea about compatibility with Cromemco, or if it is IEEE 696.  It uses a 16L8A PAL.

The company name is/was "KepTronix" out of Maryland.  I'd be happy to copy and share the documentation with anybody who is interested.

I think that one of the reasons I never tried to build the bare board was the cost of 62256 chips.  With the Alliance AS6C4008 (static 512x8) so easily available, why go with 62256?  Or is there something I'm missing about the 256KZ?  I know almost nothing about them even though I run a number of them in my Cromemco systems.

Roger

[Rich Camarda]

Using it for Z80 Cromix, the 256KZ is unique. I don't think it would be that easy just to substitute the ram chips. It would take some design work, at least what I can see form the schematic, and use of the PAL.

Anyway, it would be nice to have a more modern version of the board if it works exactly like the 256KZ. Generally when I do a "reproduction" it is 99% the same board. A board using the 62256 chips, or others, with a new design would be more like an "equivalent", which again, would be useful if functionally the same.

Rich

[Emil Sarlija]

If a new RAM board were to be made for Cromemcos, it would make more sense to design it from scratch using higher density SRAM chips. One could than have all banks filled on one card. I thought about doing this but work gets in the way of free time, rendering it just a daydream. :-/

- Emil

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[randy482]

Repro would be nice but parts would be a big issue. an equivalent board could fill several shoes beyond Cromix.

The Altair 8800c could use a DRI compatible board that at most would need reflashing a CPLD.

After more consideration making a 512K board out of 32k chips is a poor idea, better to go 8 larger chips where the 1st 64K of each chip is a Z80 bank but be IEEE for the whole RAM for 68K etc.

Some repro boards aren't reasonable. for large scale use.

Randy

[Richard Muse]

I assume all are aware that John Monahan's 4Meg Static board works with 68K 20, 30 and 40 series Cromix with a DPU, XPU or XXU with 1 jumper wire added to the 64FDC. It does not do bank select so will, of course, NOT work with the ZPU. I have this board running in an XXU, XPU and a DPU system.

http://s100computers.com/My%20System%20Pages/4MG%20Static%20RAM%20Board/4MG_RAM%20Board.htm

Richard

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[randy482]

For me at least the issue is the older Altair/Imsai bus and having an MMU to support bank switching. The z80 Cromix and the DRI bank switching isn't compatible but using a CPLD should be doable with a jumper setting. 68K Cromix is supposed to work just fine with any IEEE-696 RAM.

Randy

[Rich Camarda]

Yes, I have used that board also with the 68000 Cromix. It won't work with the Z80 Cromix however, which us where the unique 256KZ comes in.

Rich

[Roger Hanscom]

Hi All,

Just to complete the loop on this:  I found my Z80 Cromix diskettes!  My build of Rich's reproduction ZPU works perfectly with Z80 Cromix v. 11.27.  So I've checked it out with all three operating systems that I normally use:  ITC CP/M 2.2, CDOS, and Z80 Cromix!!  Great PCB!

Roger