Exploring H89-Z37 (Norberto's board)

[Mike Cassidy]

New to a just acquired H89.   Reading up on possible future enhancements - Norberto's Z37 controller board high on the list.  Appears that MTR90 ROM and a secondary address decoder ROM are required firmware in the H89.  How does one go about upgrading from MTR89 (in my unit) to MTR90 - buy proms and burn them with the code?   Is the code available?  I only see source listings

Mike

[glenn.f...@gmail.com]

Hey Mike!  So here’s an outline/brain dump but not a step-by-step

 

• Yes you’ll need to move to MTR90 to handle the soft sectored controller
• I suggest you read through the Z-89-37 install instructions https://sebhc.github.io/sebhc/documentation/hardware/HZ89/Z-89-37_Ins_Op_Sc.zip
• It is also good to familiarize yourself with the Configuration Guide https://sebhc.github.io/sebhc/documentation/hardware/HZ89/H-88-89-90_Cnf.zip
• You probably don’t need to do anything to the power supply but feel free to check back here with questions.
• The MTR90 is a 4K ROM so you will need to reconfigure jumpers (see install doc above, however see discussion below regarding CF boot ROM).
• The MTR-90 ROM is archived here: SEBHC Software Home
• You’ll need two 2732 EPROMs and a programmer. The original Heath MTR-90 was part number 444-142.
• The reason you’ll need the second EPROM is because you are using the ROMmable CF boot code at 020.000. You’ll burn that in the second EPROM. It will replace the 2516 you have there now (you can’t mix the 2516 and 2732 on the CPU board – both must be the same), however we’ll need to have a discussion on how to set the jumpers
• You’ll also need to upgrade U516 to part number 444-83. I’m not sure if we have a modern equivalent or rely on older versions that people have – hopefully someone here will clarify where to get the 444-83 or how to make one…
• The documentation on MTR90, and source listing are here: https://sebhc.github.io/sebhc/documentation/hardware/HZ89/MTR-90_Ref_ROM.zip

 

Digest that for a bit and we can discuss further

 

• Glenn

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[Joseph Travis]

Correction regarding the power supply... The 78M05 (T03 package) mounted on the aluminum "heat sink" needs to be upgraded to a 78H05.

Joe

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[dave...@gmail.com]

• “You’ll also need to upgrade U516 to part number 444-83. I’m not sure if we have a modern equivalent or rely on older versions that people have – hopefully someone here will clarify where to get the 444-83 or how to make one…

“

 

I am all setup to build the soft-sector controller PCB too.

 

Is this 44-83 a killer to the project? What is a 444-83?

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[Mike Cassidy]

According to Heath parts cross reference, the 444-83 is a 18SA30  32X8 PROM.   So far, a web search has not produced any references.  Hopefully others here have found a solution

 

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Regards,

Mike Cassidy

[dave...@gmail.com]

I was reading through the Zenith H89/90 manual (Apparently the Heathkit Manual right are owned by somebody, so those Heathkit Assembly and schematic manuals are NOT available.  The Zenith manuals are pretty much the same.  Anyway, I was ready the Zenith manual and it appears those chips, U516/U517 are 20 Pin ROMS.  I would imagine and adaptor PCB could be made, even hand wired, pretty easily to allow for a more common EEPROM to be used, if that assembly would physically fit.  Does anyone have the updated memory address lookup code to burn in to the ROMS?

 

-Dave

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[dave...@gmail.com]

My bad< I think that is only a 32-byte prom?  Hard to use a more modern part.  It only uses 5 address lines, so it can only address 32 bytes.  It’s a memory address matrix, so it doesn’t need more I, guess.

 

Interesting:

I guess you could use a more modern EEPROM wasting a huge amount of its space pulling the extra address lines low or high?  I am literate enough in EEPROMS to fully understand this.  A GAL can also do this job?

 

Surely, someone has already engineered a replacement for U516 in order to make H/Z90’s out of Z89/H89s?

 

-Dave

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Mike Cassidy

Sent: Tuesday, November 11, 2025 9:49 AM
To: se...@googlegroups.com

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[Peter Higgins]

444-83 is a 74S188 bipolar ROM with an access time of 25ns, which is much faster than what most EEPROMs are capable of. The 74S188 can still be found with a bit of searching, but you need a vintage programmer capable of programming these old fusible link ROMs.

As already pointed out, a GAL (with an adapter) programmed to produce the same logic output might work, and would have sufficient speed for this application.

[dave...@gmail.com]

“a GAL (with an adapter) programmed to produce the same logic output might work, and would have sufficient speed for this application.”

 

That’s a great idea.  I am not one to know how to write a program for a GAL – lol.  I have programmed GALS before as replacements for a similar device in Commodore 64s.  That’s not hard.  You got to have someone more knowledgeable that me to know how to create the lookup table code.  After next year, when hopefully, I will have more time, I could look in to it more.

 

I would be surprised that someone has not already done that.  But then again, The H89 probably didn’t sell in the millions and millions like the C64 or Apple II did.  You can get anything you can possibly think of for those machines.  There are tons of YouTube support for those.

 

I started out with building an OSI Superboard II system and the upgrading it’s memory, adding a floppy controller and a C1P case.  OSI is ghost land when it comes to support or availability.  Not many of us had them, I guess. 

 

Then I built an H89.  After that, while others were going IBM PC Clone, silly me went RS Model 4 with 128K of memory.  If I recollect correctly, I could run CPM in one 64K memory location, and then Flip to TRSDOS in the other.   SuperCalc (or some spreadsheet in one memory segment) and Wordstar in the other.  I was multi-tasking before Windows – lol.  I was never in to games, always programming, or documenting in Wordstar.  My memory is bad from the 80s so take some of this with a grain of salt -lol.

The First PC Clone I had, if I recollect correctly, was a Heathkit 386 machine.  I also had an H161 (?) with dual floppies in the pop-up and a $700 10MB Hardcard installed.  I do not remember what happened to that machine. It was HEAVY, but I had a portable computer.

 

I think this is why I want to get this H89 that I bought at Goodwill working. Hopefully, it will help bring back memories that have long been in deep grey matter storage.

 

-Dave

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[Joseph Travis]

I believe I have some 444-83s in my inventory and I have the ability to program the 74S188. Email me directly when the time comes.

Joe

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[glenn.f...@gmail.com]

A Goodwill H89. Wow. Cool find!  This group is great at helping folks like you.  We also have an SEBHC Discord channel if that’s more to your liking.

 

Good luck!

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[glenn.f...@gmail.com]

Quest seems to have them (?):

DM74S188N Integrated Circuits NATIONAL SEMICONDUCTOR CORP | Quest Components

 

This one shows 35ns…

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Peter Higgins

Sent: Tuesday, November 11, 2025 10:48 AM

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[Peter Higgins]

On Tuesday, November 11, 2025 at 9:43:56 AM UTC-8 Glenn Roberts wrote:

Quest seems to have them (?):

DM74S188N Integrated Circuits NATIONAL SEMICONDUCTOR CORP | Quest Components

 This one shows 35ns…

That was likely the speed version used for the 444-83, and should be fine.

[Mike Cassidy]

Also located a source for 74S188 at futurlec.com

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Regards,

Mike Cassidy

[Joseph Travis]

My sincere apologies to Dave and Mike, I should have verified my inventory before I spoke up.  I have just one 444-83 (that I'll keep as a master) and no 74S188s.  I didn't realize that I had gone through all of them.

It appears some of you have found a supply of the 74S188s.  If you were to buy some and send them to me, I would be happy to burn a 444-83 for you in exchange for a 74S188 + shipping.  If you allow me to keep more than one, I'll pay the shipping back to you.

Joe

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[Mike Cassidy]

Thanks Joe.  Ordered two earlier today.  Will send your way when they arrive along with return postage.  You can send your address off the site - cmc...@gmail.com

Mike

Regards,

Mike Cassidy

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[dave...@gmail.com]

Discord is something my whipper snapper kid is in to – LOL.  No, I have discord too, I’m just not use to going there that often.  I am mainly on channels for YouTube “stars” have a few others.  I will have to join SEBHC later today; thanks.

 

-dave

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[dave...@gmail.com]

My T48 programmer (fairly modern) can’t handle them.  I do not have an old programming.  We need 25ns?  If 35ns will do, I am happy to order them, if someone can program them, or if I can get a programmer (he who croaks with the most tools wins), that would be great.

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[dave...@gmail.com]

I’ll get some on order now <grin>

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[norberto.collado koyado.com]

I will double check if I still have any spares 444-83.  Yes, we have the 444-83 in GAL format as well, but you will need an adapter to make it work and I do not have any at this time. 

Also, you will need to update the other two 20-pin ROMs with later version as well.

Norberto 

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[glenn.f...@gmail.com]

True and worth checking but if you’ve got MTR89 you probably already have 444-66 and 444-61 (but, again, need to check!)  see configuration guide document I posted earlier….  If you’ve got an older machine and/or MTR-88 you may need all 3…

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[dave...@gmail.com]

I ordered (6) six 74S188s.  Will they work for the others?  If not, what GAL chips do we need?  Do GALs go fast enough?

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[Lee Hart]

The 444-83 address decoder is a 16-pin 32x8. The other CPU board PROMs are 20-pin 256x8.

I too have a programmer for these old PROMs. There are quite a few brands and part numbers that all have the same pinout and would work. If someone has some of them, I'd be happy to program them for you.

I'd also be interested in buying a few 74S188s or equivalent. I have several H89 CPU boards with the older PROM that I could upgrade.

It's not strictly necessary to upgrade the 5v regulator from a 78M05 (3 amp) to a 78T05 (5 amp). However, it gives you more 5v current, especially useful if you have floppy drives mounted inside. But it's important to remove the two yellow wires from power supply board connector P101 to directly connect to the bridge rectifier on the metal heatsink. The pins in P101 are only good for 3 amps, and will burn up if you try to pull 5 amps through them.

Happy hacking,

Lee Hart

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[Mike Cassidy]

I checked and I do have 444-61 and 444-66 installed.  I've just sent a PROM to Joe to be programmed as the 444-83.  So this is a start in moving to MTR90.

Thanks all

Mike

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Regards,

Mike Cassidy

[norberto.collado koyado.com]

MTR90 upgrade is the right path to do. I loved to use Hex with the MTR90 as it is easy to debug.

Norby

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