Plotter ROM for the HP9810 - how to use it?

[Thomas Falk]

Hello,

I have a HP9810A, a plotter HP9862A and a ROM 11261A "Plotter Printer Alpha".

I know that this ROM does allow to print alphanumeric characters on the printer for the HP9810 using the <FMT><FMT> key sequence. I can see from the descriptions of the corrsponding plotter ROM for the HP9820 that it allows to draw characters and scale the plotting area.

Does somebody know what this ROM can do at the HP9810 for the plotter and how to access it?

Best regards,

Thomas

[simon]

Hello Thomas,

I also have HP9810A, unfortunately not working. Do you know where a circuit diagram could be sourced for this calculator?

Regards, Paul

[Tony Duell]

Am I allowed to 'blow my own trumpet' here ?

There is a fair amount of information on the HP9810 on the Australian HP museum site (URL is as this site, but .net rather than .org).

There should be a manual for the plotter ROM. The HP9810 service manual is there, but be warned it's mostly a 'boardswapper guide', the only schematics are for the PSU. And if you can stick my writing, there's a full schematic.

HPCC published a set of articles on repairing these machines too.

[simon]

Thank you very much, it's great help.

Cheers

[Tony Duell]

If you have any problems with this series of machines, feel free to ask me. I have done a number of repairs to component level on them.

If you want the HPCC articles (in \LaTeX), please ask me. They may explain some less-obvious bits of the machine.

[Thomas Falk]

Hi Simon,

because Tony has already answered, I don't have to point in his direction.

One addition: If you have to dive deeper in the machine, I recommend the study of the patent 3859636. It describes the HP9810 in every detail down to the micro code and includes overviews, schematics and listings on the system. Hopefully you will not need it, but in my case I found two failing bits in one of the microcode ROM at the end of three months work.

If you have questions, you may also ask me. Where are you from?

Best regards,

Thomas

[waterlander2004]

Hi Thomas,

Good to see more interest in the 9810! It is a beautiful machine, and thanks to Tony's enthusiasm and expertise, I found out about it a few years ago too.

Now being a 98xxx fan (and in the process of trying to fix a 9830 with suspect ROM board), and out of interest, how did you fix the failed microcode ROM problem on your 9810?

Kind regards, Eric

[Thomas Falk]

Hi Eric,

(04-19-2014 11:44 AM)waterlander2004 Wrote:  how did you fix the failed microcode ROM problem on your 9810?

This was easy: I have found that only one bit was wrong at a certain address. It was stuck at H. Therefore I decoded out this address and pulled the bit down. This was done using a 74HCT688 decoder and a AND-Gate made by diodes. The resulting fix is shown in the following picture.

   

Finding this was a little more difficult. When I started to repair this calculator I found a dead logic gatter and a dead transistor in the drivers for the DRAM ciruits. After repairing this it worked, but the display was wrong.

In the end I read the addresses and the data of the microcode ROMs and found the faulty bit. Actually after having done this it is quite easy: If you read the adresses and the data during running the calculator you get a partial dump of the mico code ROMs. You will get the data for the adresses the calulator is accessing only, but this is enough. This data you can compare with the listing of the ROMs in the patent US-3,859635 describing the calculator. My work place looked like this:

   

There are two logic analyzers in use. For comparing the read data and the data from the patent I wrote some small python scripts.

If there are more faulty bits in the ROM the fix above is not practicable and you would have to replace the ROM by some modern or older parallel EPROM. This should be possible.

When I repaired my HP9810, it was my only device. I got reference data from the HP9800e emulator and compared its program dumps with the data from my calculator to dig down to the micocode. To isolate a faulty card it is useful to have a second calculator for board swapping.

I have now a HP9810 and a HP9820, if somebody needs some material to swap for error search, I may be able to help. Just ask.

Best regards,

Thomas

PS: I will show this calcuator and its plotter in use at the VCFE in Munich at the begin of May.

[waterlander2004]

Thank you Thomas,

A very smart and elegant solution. Indeed not practical for a ROM board with multiple failing parts, which is what I'll need to establish next... But perfectly doable in your situation!

Thanks for sharing your approach, good to keep in mind!

Kind,regards, Eric

[Tony Duell]

(04-19-2014 08:45 PM)Thomas Falk Wrote:  Hi Eric,


This was easy: I have found that only one bit was wrong at a certain address. It was stuck at H. Therefore I decoded out this address and pulled the bit down. This was done using a 74HCT688 decoder and a AND-Gate made by diodes. The resulting fix is shown in the following picture.

I think I should point out that there are 2 levels of firmware in these machines. The microcode is part of the CPU and is part of the system to interpret machine instructions. It consists of 256 words, each 28 bits long, and is the same in all HP9800 machines (AFAIK, I have never seen an HP9821 inside).

The system firmware is what makes the machine behave as a calcualtor. It consists of 16 bit machine instructions -- 2K words in an HP9810, 4K words in an HP9820, and 7.5K words (IIRC) in an HP9830.

The microcode is stored in 7 bipolar ROM chips (each 256*4 bits) on one of the CPU boards. The system firmware is stored in HP custom ROM chips, each 512*8 bits.

(04-19-2014 08:45 PM)Thomas Falk Wrote:  Finding this was a little more difficult. When I started to repair this calculator I found a dead logic gatter and a dead transistor in the drivers for the DRAM ciruits. After repairing this it worked, but the display was wrong.

In the end I read the addresses and the data of the microcode ROMs and found the faulty bit. Actually after having done this it is quite easy: If you read the adresses and the data during running the calculator you get a partial dump of the mico code ROMs. You will get the data for the adresses the calulator is accessing only, but this is enough. This data you can compare with the listing of the ROMs in the patent US-3,859635 describing the calculator. My work place looked like this:

I have a commented source listing of the microcode (not the system firmware), produced in part by desoldering the ROMs from a working machine, reading them, and figuring out what was going on.

(04-19-2014 08:45 PM)Thomas Falk Wrote:  There are two logic analyzers in use. For comparing the read data and the data from the patent I wrote some small python scripts.

If there are more faulty bits in the ROM the fix above is not practicable and you would have to replace the ROM by some modern or older parallel EPROM. This should be possible.

The microcode ROM has to be quite fast. Remember the CPU clock is 8MHz, giving a 125ns cycle time. In one cycle the microcode program counter has to update, the microcode ROMs have to give the next word, and the decode logic has to work too. Many EPROMs would be nowhere near fast enough for this.

There were fusible-link ROMs with the same pinout as the CPU microcode ROMs. I suspect NOS ones do turn up from time to time, obviosuly these are strictly OTP, so ex-equipment ones are useless.

The system firmware ROMs (where Eric is having problems) are more difficult. HP's ROMs are a bit strange, no standard PROM/EPROM will just drop in. There are, of course, various work-arounds.

(04-19-2014 08:45 PM)Thomas Falk Wrote:  When I repaired my HP9810, it was my only device. I got reference data from the HP9800e emulator and compared its program dumps with the data from my calculator to dig down to the micocode. To isolate a faulty card it is useful to have a second calculator for board swapping.

I will pretend I didn't read that. Suffice it to say I can think of a dozen faults where
board-swapping will cause confusion, and some wehre it will cause damage!

-tony