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Single Board Computers

The board photos show that the firm's name was "Molecular Computers", which is a different firm than the one I'm thinking of. Besides, I think Molecular bit the dust around 1983-84. Still, you mgiht dump the EPROM to see what this thing really is.

As far as the other board's monitor goes, you might see what the program listing says. It could be that you have the syntax of the command wrong (I've banged my head a few times on that one).
 
Okay. To dump the EPROM I am assuming that I need an EPROM burner. Do I need a certain type of burner, because I have no clue what type of chip it is?

Here is an excerpt from the manual:

D (Start adr),(End adr (optional)) (cr)

Displays memory in hex from starting address to optional ending address. If no ending address is selected, 256 byte block will be displayed. A CTL-S freezes the output and a second CTL-S causes it to resume. Any other key depressed terminates the displayed output.

I have entered D0000 into the computer and it displays 2 lines of the memory contents. If I type something in with a larger argument it freezes (I first noticed this when I typed in D0000,FFFF, but it does it with much smaller ranges too and with only a start address specified). I have tried CTL-S and the no-scroll button on the terminal but that does not help. I also have tried pressing other keys and it does not return to the prompt. The reason why I think that the cause could be that the EPROM lost some data is because when I use the S command (it dumps one memory location to the screen and allows you to change it) without changing the value, I find some larger blocks of 00 in the returned data. I also double checked and the returned contents from the EPROM end around CA00, not CE00.

I have successfully executed other memory operations such as fill the range of memory with the specified byte. I have not tried the move contents command yet. I did try the run user program command, but it froze. I believe that the reason for that was because I did not have any program at the address I specified.

I have some more news. I was experimenting with the monitor program a bit more, and I found out that if I press the no-scroll button a couple of times, the monitor continues to list the memory contents. Some of the lines though are not completely dumped to the screen and are ended with the gibberish character. Sometimes though, the readout will continue and the console will display some numbers mixed in with the gibberish character. I am not sure if this is a terminal problem or a problem with the monitor program. After that the monitor may act a bit strange, but I believe that it has something to do with pressing the no scroll button. After a while the behavior returns to normal. I do know that it when it does display the memory contents the displyed bytes are correct. I also checked the PSU's output voltage, and it reads 15v. The manual says that it should be 12. That might be a cause for the improper output.
 
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Well, it could be that there's a bug. Another possibility is that your memory is parity-checked and you're running into a parity error trap. I assume that you've tried a space between the D and the address.

Most likely, the EPROMs on both these things are 2764, 27128 or 27256 types. That would be approximately correct for a 28-pin EPROM for the time.
 
I just reviewed the ebay listing of that computer, and I found that it sounds like the seller might have had the same problem:
Recently tested, signed on with required baud rate. BIOS testing for several functions returned lines of code on each function 4,6 but no ASCII characters. As if baud rate was wrong on return but maybe picked up end of line character for displayed information. Numbers of lines of code returned depended on which BIOS functions such as memory dump, memory test, etc. No other testing was done.
Click to expand...

Having the bug is not too big of a deal to me, I am more interested in preserving the contents of the EPROM so it is not lost. The monitor will not allow me to type a space after the command. It displays a new line and asterisk then the prompt on the new line.

What exactly is a parity error trap. I understand what parity is in relation to serial communications, but I never knew it existed in memory.
 
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Parity uses a bit(s) stuck on the end of a word to indicate the parity of the data byte(s). So, for an 8-bit byte that was even, you recorded a 1 in the 9th bit for parity. The IBM PC used it, but just halted if a parity error got trapped. More useful variants of this use more bits per word, allowing for automatic correction of 1 or even multi-bit errors. Real popular with the server crowd.
Most modern readers should be able to read them, but maybe not burn that type of EPROM, but that shouldn't really matter. If you don't have one, you can usually pick up basic ones pretty cheap on eBay. Or I'm sure someone here would be more than happy to archive them. I found a flyer on the web for the bigger board. Tomorrow I'll see if I can decipher the part no. on the EPROMS.
patscc
 
Thanks. I have the schematics for the board too if you are interested in seeing them. I could scan them. I also found a contact info page for Business Information Systems. I think that I will try to contact them sometime this week or next.

I tried turning off the Auto XON/XOFF feature of the terminal, and the memory dumped continuously, but it still displayed the gibberish character. I think that it has to be a bug. I just changed the jumper settings for the baud rate, and the system is running perfectly when I do the D command. Although I have it set to 9600 baud, the system is using 1200 baud. I might have made a wrong connection.
 
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Another update: I did have the jumper settings set incorrectly when I ran the above test. I did try to use the monitor's auto baud rate detection, but that did not work too well (it still was at 1200 baud and the terminal at 9600 baud). I may have to check other jumpers to see if there is any conflict. I reset the jumpers back to 9600 baud and the monitor would not dump the RAM contents properly. I do believe that there is some sort of bug in the system.
 
I am still working on scanning the schematics, but I would like your guys' opinion on selecting an eprom programmer. I did an ebay search and tons of different types appear. I am aiming for a higher quality one because I do not want to trash the eproms and their contents. Here are the two that seem to come up the most:
http://www.ebay.com/itm/NEWEST-Will...575?pt=LH_DefaultDomain_0&hash=item43b405625f
http://www.ebay.com/itm/TOP853-USB-...202?pt=LH_DefaultDomain_0&hash=item3f1c60fe1a

What do you think of those, or would it be best to get a vintage burner? I am just really afraid of loosing the contents of the chips if I get a bad burner. Also just a quick question about eprom burners. Is there any way to write protect them so I do not accidently press the wrong button when I am reading the chip?
Thanks.
 
I have a Willem, and it works pretty good. It's hard to do anything like accidentally burn a EPROM in it, so you should be good to go.
I don't think you can overwrite a EPROM, once it's burned, you can't access the gate electrode in the cell, which is why you need to erase them with UV first.
It's got so much more flexibility than older burners since it does FLASH and other types.
patscc
 
I've had the best luck with used professional-quality programmers. A lot of the old gear is being ditched for good prices because of several factors:

(1) Nobody uses UV EPROMs any more, except to mainain old hardware--and that's vanishing.
(2) Modern PCs lack real parallel or serial ports used to interface to the old programmers.
(3) The old gear doesn't support more recent devices.

So, for instance, a Xeltek Superpro programmer might be had for $50, which makes it a better deal (if you have an older system to drive it with) than any new kit, with the benefit that the programming software (1) runs on DOS or at worst, Windows 3.1 and (2) has been thoroughly field-tested.

Much easier than trying to work your way through someone's Chinese. On the other hand, if you're looking for a decent modern unit and don't have unlimited funds, I've recommended the Wellon programmers as being a slight notch above the run-of-the-mill Far East stuff, followed by Genius, followed by the TOPxxx stuff. A glance at eBay shows lots of choices.
 
Thanks for the suggestions guys. I think the Willem one is at the top because there is one for pretty cheap, and because it supports many different chips, but I will definitely look into some of the older professional ones too. I have several computers that could support one. An XT, and XT clone, an AT, and a few mid to late 90's towers that have parallel and serial ports on them.

MikeS, I do not know if the sockets in my computers would support it.
 
For the SBC-2001 the EPROM is a 2532, according to the parts list (the label covers up the chip number in addition to the window so I have not read the number directly from the chip). There is also another chip on that board that is a 74S288 memory mapper ROM.

For the other board, the label completely covers the chip, and I do not wish to damage the label because it has some sort of number on it that might be helpful in the future. The printing on the board says 2732 next to an outline of the chip. There is a larger outline that surrounds the smaller outline that says 2?64. I think the ? is a 7, but there is a via right there, and the solder covers the number almost completely. There are also several smaller chips on the board with labels on them. I do not know if those would be ROMs or not.
 
The smaller chips with labels might be PAL's. 2532's (should be a TI part) and 2732's are both EPROM's, though not interchangeable. The larger outline is probably for a 2764. The labels may, if the case is not plastic, cover the erase window, so you want to keep them on.
The Willems should read the 2532 and 2732, but check the manual for exactly what families are supported on their website.
The 74S288 is a TTL fusible link PROM. I don't think the Willem will read this, but I could be wrong.
patscc
 
Thanks for the advice. I will be sure to check their website out.

I am not too worried about the PROM since those don't lose their memory over time like an EPROM can (unless I am mistaken). The manual has a listing for that PROM but it looks more like a table than a listing of code.
 
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