HP9831 System ROM


Peter ONeill
 

After getting my replacement system ROM board working for the 9825A, I been testing it for a few days to make sure it is reliable.
Having nearly completed the PCB design, I decided to start testing the system code for the 9831. It boots with no error, it allows me
to store BASIC statements, but when I try to run a one line program to print "Hello World" it gives me an ERROR 1 "Plug-in ROM Missing", similarly
if I use the FETCH key, enter the line number and press EXECUTE I get ERROR 1 rather than the program line.

Both the 9825A and 9831 binaries are in the files section here, the 9825A binary works but the 9831 gave the above errors. Does the 98218
ROM have to be installed even though I'm not using a disk drive?

Regards,
Peter


Dyke Shaffer
 

Peter,  that would be a good question for my old roommate in Loveland ( circa 1978 ), Art Boyne, he did the port / rom release for the 9831, saw that his linked in profile shows 'retired', wouldn't that be something if he responded,   Dyke


 

No, it should work without it, at least mine does.

-Rik


Peter ONeill
 

Thanks Rik, as I've been unable to fault the 9825A binary so far, so I think my hardware is okay, so I'll verify the EPROMs again and if they check out then 
then 9831 binary code may not be 100% ok. By the way the same errors occur with or without 9825 option ROMs plugged in.

One thing I forgot to say in my original post that when I RUN some code the ERROR 1 says that the error is in line 24567. That may not be the exact line number but the number is the same every time.

Peter.


Peter ONeill
 

Dyke, yes it would. Only today I was reading about Art and the 9831.

Peter


Dyke Shaffer
 

Peter,  what I recall is that the 9831 port from 9830 was a quick turn project, perhaps as short as a month or two, and that probably meant that the 9830 system / option rom partition would have been preserved within a single combined release in the 9825 language rom drawer.  If it's not an error in the image or programming, could become a real mystery,  Dyke


Paul Berger
 


On 2021-03-04 12:18 a.m., Peter ONeill wrote:
After getting my replacement system ROM board working for the 9825A, I been testing it for a few days to make sure it is reliable.
Having nearly completed the PCB design, I decided to start testing the system code for the 9831. It boots with no error, it allows me
to store BASIC statements, but when I try to run a one line program to print "Hello World" it gives me an ERROR 1 "Plug-in ROM Missing", similarly
if I use the FETCH key, enter the line number and press EXECUTE I get ERROR 1 rather than the program line.

Both the 9825A and 9831 binaries are in the files section here, the 9825A binary works but the 9831 gave the above errors. Does the 98218
ROM have to be installed even though I'm not using a disk drive?

Regards,
Peter
_._,_._,_


I guess it is possible something went wrong when I dumped the ROM I never did test it, I stil have the 9831 system ROM and I will give it a go later today.

Paul.


 

Peter,

 

I looked at the pictures of my 9830A and I noticed the add-on board on the memory connector.

I haven’t looked to the function of it, but I remember, at a certain moment one of the 1820-1255 (SN74368) was defective and this slowed down the 9831A huge.

If I can find sometime I’ll make some pictures of both sides of the PCB .

 

-Rik

 

 

Van: VintHPcom@groups.io <VintHPcom@groups.io> Namens Peter ONeill
Verzonden: donderdag 4 maart 2021 12:08
Aan: VintHPcom@groups.io
Onderwerp: Re: [VintHPcom] HP9831 System ROM

 

Thanks Rik, as I've been unable to fault the 9825A binary so far, so I think my hardware is okay, so I'll verify the EPROMs again and if they check out then 
then 9831 binary code may not be 100% ok. By the way the same errors occur with or without 9825 option ROMs plugged in.

One thing I forgot to say in my original post that when I RUN some code the ERROR 1 says that the error is in line 24567. That may not be the exact line number but the number is the same every time.

Peter.


Peter ONeill
 

Hey Rik, that's interesting. I had a close look at your photos and apart from the three 74368 inverting buffers, the 1820-0068 is a 7410 and the 1820-1112 is a 74LS74, so no complex logic there. The PCA number is 09831-66529 so the board is specific to the 9831. My 9825A has the same connector plugged into a piece of PCB material with no traces, I assume to stop it flapping in the breeze. This looks like a way of identifying that the hardware is a 9831 rather than a 9825A. Possibly, this would. explain the ERROR 1. Also if the binary image was corrupt I would expect the software to crash rather than consistently giving error messages on certain operations and then being able to get the system prompt back by pressing CLEAR or RESET.

Hope you get a chance to take some clear images of both sides of the PCB.

Regards,
Peter


Paul Berger
 


On 2021-03-04 6:35 p.m., Peter ONeill wrote:
Hey Rik, that's interesting. I had a close look at your photos and apart from the three 74368 inverting buffers, the 1820-0068 is a 7410 and the 1820-1112 is a 74LS74, so no complex logic there. The PCA number is 09831-66529 so the board is specific to the 9831. My 9825A has the same connector plugged into a piece of PCB material with no traces, I assume to stop it flapping in the breeze. This looks like a way of identifying that the hardware is a 9831 rather than a 9825A. Possibly, this would. explain the ERROR 1. Also if the binary image was corrupt I would expect the software to crash rather than consistently giving error messages on certain operations and then being able to get the system prompt back by pressing CLEAR or RESET.

Hope you get a chance to take some clear images of both sides of the PCB.

Regards,
Peter
_._,_._,_


I just fired up my 9825A, which does not have that card, with a known good 9831A OS ROM and I don't get those errors that you saw.

Paul.



Peter ONeill
 

Paul, till a few minutes ago I thought I'd fixed the issue. I made one change to my board and the 9831 code started working without the ERROR 1 after switching the machine off changing the jumper for the 9825A code and testing that, then changing back to the 9831 it is giving the error again. As I have an additional 200mm of ribbon cable between my board and the system ROM socket I may look at terminating the address/data lines or as the input and output buffers are separate devices try powering the output buffers from 6V so I'm not running them at the absolute maximum of 7V. Currently I'm using 74LS240 inverting buffers and unlike the 98228 clone which drives a pair of BIBs on the ROM interface board I'm driving quite a way back to the processor. For now I think the issue is with my design not the 9831 binary image.

Regards,
Peter


Paul Berger
 


On 2021-03-04 11:43 p.m., Peter ONeill wrote:
Paul, till a few minutes ago I thought I'd fixed the issue. I made one change to my board and the 9831 code started working without the ERROR 1 after switching the machine off changing the jumper for the 9825A code and testing that, then changing back to the 9831 it is giving the error again. As I have an additional 200mm of ribbon cable between my board and the system ROM socket I may look at terminating the address/data lines or as the input and output buffers are separate devices try powering the output buffers from 6V so I'm not running them at the absolute maximum of 7V. Currently I'm using 74LS240 inverting buffers and unlike the 98228 clone which drives a pair of BIBs on the ROM interface board I'm driving quite a way back to the processor. For now I think the issue is with my design not the 9831 binary image.

Regards,
Peter
_._,_._,_

Well I am in the process of building my own, I would be done but a piece on the light over my work table broke and I had to take time out to turn a replacement.  I will probably finish it up tomorrow as it it get very late here. 

You do know that there are TTL chips that are functionally equivalent to the BIBs, except that the direction function is reversed and the pinout is not the same I am going to use 74LS640s, they are just like an inverting 74LS245.  I have not decided what I will use for address latches yet but I have a good stock of TTL to choose from.

Yes you long cable could be an issue however I encountered problems trying to extend the memory bus on my 9835 when I was designing a RAM card for it.  When I was building prototypes for ROM modules I made an extender that just barely bring a ROM slot outside the machine.

Paul.



Dyke Shaffer
 

Peter,  something easy to try as an experiment, not necessarily a fix is to emulate a ground shielded ribbon cable.  Turns out significant relief is available when 'shared area coupling' is encountered ( per unit length degradation in signal integrity in ribbon cables with sparse ground returns ) when  a conductive surface is placed ( copper clad pcb for instance ) in as close proximity to the plane of the ribbon cable suspected of being a root cause.  It's a long winded description of an observation made long ago that an 'equipotential surface' merely need be present ( closer the better the geometric planes formed by the ribbon cable and the surrogate ground return path ), that is not otherwise connected, just properly positioned.  Similar thing is accomplished by making the ribbon cable shorter in that both reduce the 'shared area' between loop currents ( di / dt phenomena )

If signal integrity is the issue, the long ribbon cable is more likely to succumb to 'shared area' coupling than 'shared impedance'.  Series termination is one way to slow down the edges, however, it seems to take a lot of R to begin to see improvement in TTL interfaces which can begin to produce DC offsets ( if I remember all this correctly )  good luck with testing,  Dyke


Peter ONeill
 

Thanks Dyke, this is one of the things I had considered and is on my list try. I have some adhesive backed copper tape here in my lab, so it will be easy to test. The only reason the board is connected by a ribbon cable is ease of access while I'm debugging the hardware. Now that I have seen the the 9831 code work once I'm more confident now that I have a signal integrity issue rather than some corrupt bits in the binary image.
Regards, Peter.


Peter ONeill
 

I have now stopped the ERROR 1 issue, but I still need to do some further testing to make sure that it is reliable.
Dyke suggested a ground shield for the ribbon cable, and this was easy to try quickly I tested this and it made no difference, a least I was able to rule this out as a cause as in the board design has no ribbon cable.
One thing that has been nagging at me for a while is that the output buffers can only drive to a maximum of 5V and as I'm using 74LS and in the final design 74ALS the logic highs won't be +5V. Also the output buffers are driving the lines all the way back to the processor not locally to the BIBs on the ROM interface board. Further, I noticed that on the Option ROM side of the BIBs on the ROM interface the address/data lines have 2k2 pullups to +5V. So, I thought I'd try adding some 2k2 pullups
to my prototype to give the output buffers a bit of help and bingo now it seems to work.

Thanks to everyone for their input.

Regards, Peter


Jack Rubin
 

Peter,

I've had a chance to do a brief search for my orphaned 9825A system ROMs with no luck so far. I'll continue to look next week, but it sounds like you're way beyond needing them at this point. Still, it will be good to locate them.
--
Jack
www.computerarium.org


Peter ONeill
 

Jack, while I now have my replacement system ROM working an original ROM pack would complete my 9825A, there is one on ebay but it's just the board, no enclosure. So if you find it I'm still interested.
Regards, Peter


Jack Rubin
 

I'll let you know - I'm sure it's in a very safe place. :>)

--
Jack
www.computerarium.org