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Terminal computer

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Philcogrump

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I have what I believe is a homebrew terminal computer, which uses the DB-25 RS-232 port to some mainframe (no idea what it was). The terminal looks like a keyboard in a metal case with a power on/off button, and the board inside looks like it was perhaps designed for a S-100 bus. It is labeled MOSTEK ASSY 450-00189-00 REV E, and has a Mostek 3870 microcontroller on it. I tried to find more information on the Internet on this board and couldn't find anything much, but I recall one website said something about this board that it was for a terminal and could be expanded to operate as a computer since the 3870 actually has a CPU, RAM, and ROM all in one chip. I'm not so sure how or the details, anyone have an idea what this is? If pictures would be helpful, let me know.
 
Doesn't really look like S-100 to me. Is the (magnified) picture actual size? The width & spacing of the 100-pin connector ain't quite right, and your connector is centered on the board, where S-100 connectors are somewhat offset. The skirt areas measure 1-1/2" & 2-1/8" respectively. Total width of the board is 10" and the connector is 6-1/4" long.

--T
 
The picture is pretty close to actual size, see how the ICs appear just the right size (depends on your screen resolution though). If it is not S-100, then any idea what it is?

Notice that the board is not using the card-edges at all, it has the power wires, keyboard input, video, and RS-232 wires all hard-wired to the board mostly through IC sockets.
 
The 100-pin connector probably is for interfacing your board to other components, like memory, etc. The J1 connector looks like it might be an alternate (video?) I/O connector, or mebbe an input from the power supply. What do the red&white and orange&white twisted pairs connect to at the other ends?
Since the 3870 is a single-chip computer, you might not be able to re-purpose it, as the 4K ROM is probably programmed as a keyboard/display controller. To re-purpose that board would no doubt require programming a whole 'nother chip. Course, I don't know why you'd want to, it sounds like it's a pretty nice terminal already (my $0.02).

--T
 
The twisted wires (red, orange and white) are for video and transmit/receive to the RS-232 port. I didn't really check what the ICs were when I had it opened up, but I think they all were normal TTL, but if these were RAM then it is likely.

I've searched online for information on anything related to MOSTEK, but not much luck (any reason why not?). By the way, this probably dates to the early 80s, if not, earlier so I'm wondering what kind of RS-232 data it uses? I tried interfacing this terminal with my laptop using Hyperterminal and never had any luck. I tried various settings, stop bits, etc etc without any success. BTW, there is a switch in the back of this terminal, and I think I read somewhere that some terminals gave the choice of half or full byte lengths or something?

For the laptop communications, I'm wondering if the 5V source is too low for this to properly communicate with the laptop? Maybe I need some pull-up resistors (say 10K) to 12V? Any other ideas on how to make this useful?
 
Philcogrump said:
The twisted wires (red, orange and white) are for video and transmit/receive to the RS-232 port. I didn't really check what the ICs were when I had it opened up, but I think they all were normal TTL, but if these were RAM then it is likely.
Click to expand...

I kinda thought the red or orange wires might be for video, I/O, etc. There are a couple of traces running from the J1 straight down to the wiring block where those wires originate, so the J1 probably just duplicates the same signals. The u12 - u18 chips are wired in parallel, like RAM chips would be.
I've searched online for information on anything related to MOSTEK, but not much luck (any reason why not?). By the way, this probably dates to the early 80s, if not, earlier so I'm wondering what kind of RS-232 data it uses? I tried interfacing this terminal with my laptop using Hyperterminal and never had any luck. I tried various settings, stop bits, etc etc without any success. BTW, there is a switch in the back of this terminal, and I think I read somewhere that some terminals gave the choice of half or full byte lengths or something?
Click to expand...
I didn't have much luck either, except that the 3870 is code-compatible with the Fairchild F8 CPU, but a single-chip implementation, with either 2K or 4K of ROM (depending which webpage you read).
I think RS-232C has always been standardized. I've seen old boards that only use three wires; Tx, Rx, & Gd. The pins for Tx & Rx can be wired either of two different ways, but they should always be pins #2 & #3 on the 25-pin D-shell connector, with pin #7 used as ground. If you can't communicate with the terminal, try swapping pins 2 & 3, it should work one way or the other. I don't know about full or half bytes, but your terminal has to be in agreement with the computer as to word length, usually either 7 or 8 bits, and the number of stop bits, usually 1, 1.5, or 2. Full- or half-duplex settings determine whether the terminal or the remote system echoes the characters to your screen (easy to tell when this is set wrong, you'll be seeing double).
For the laptop communications, I'm wondering if the 5V source is too low for this to properly communicate with the laptop? Maybe I need some pull-up resistors (say 10K) to 12V? Any other ideas on how to make this useful?
Click to expand...

Five volts should work, as the RS-232 interface usually has the pull-up already built-in (RS-232C uses 8v.). As for not communicating with HyperTerminal, why does that not surprize me?

--T
 
So I assume Hyperterminal must be a bad software to use for this purpose? What software do you recommend for PCs that works well with older terminals?

Or could I make a QBASIC program on the laptop that would open the COM port, I forget the exact command, but by using that would I be able to get the characters from that port and make a program that would act like a BASIC computer or something else, perhaps a game, through RS-232 to that terminal?
 
Philcogrump said:
So I assume Hyperterminal must be a bad software to use for this purpose? What software do you recommend for PCs that works well with older terminals?

Or could I make a QBASIC program on the laptop that would open the COM port, I forget the exact command, but by using that would I be able to get the characters from that port and make a program that would act like a BASIC computer or something else, perhaps a game, through RS-232 to that terminal?
Click to expand...

I dunno, mebbe it's just me, but I've always had lousy luck with Hyper. The only (freeware) programs I would recomend trying would be Telix or ProComm Plus, both of which are DOS programs.

Really, if you just want to hang the terminal off your PC's serial port, it is pretty simple to do from DOS, after you have the correct wiring. Under DOS, use the MODE command to set-up the com port to match the parameters of the terminal, then the CTTY command to switch all I/O to the serial port. If you don't have a DOS book explaining how to do this, get back to me and I'll try and give more details.

--T
 
I installed Telix on the IBM laptop, hooked it up with the terminal and it gives me the same thing as Hyperterminal does. The only difference is that it is much easier to use than Hyperterminal when it comes to configuration. However, all I get when I type on the terminal to the laptop are a bunch of the same characters like xxx or a weird looking C, some degree signs, or a box.

I have the port set up for 300 baud, minimum for Telix, and 8 bits with 1 stop bit. I tried different settings like 1200, 2400 baud, and 7 or 8 bits and 1 or 2 stop bits, all do the same thing. I also changed termianl devices to various types, no improvement. Any idea what to do?

EDIT: I took a RS-232 serial port monitor and found that the RD led is green, and if I hook it up to the laptop, the TD led is red. I'm wondering if the RD should be red too (need an inverting buffer?).
 
If you're getting garbage coming thru, it's usually a sign that something is configured wrong, although it could also mean something else, like a bad memory chip. Have you tried pulling/reseating the chips? Sometimes that helps.
I don't know about your breakout box, but on mine, red means that the connection is wrong, and green means that both ends are compatible with each other. F'rinstance, if I have Rx <--> Rx, the LED is red, but if it's Tx <--> Rx, it shows green. Red is usually Not A Good Thing. Could be all that you need is a null-modem.

--T
 
I'm not sure if anything is bad in the terminal because it works when you put a jumper on its own Tx to Rx, but maybe I have the cable wired wrong for the DB25 to DB9 for the laptop. Will have to look at that later.
 
EDIT: I took a RS-232 serial port monitor and found that the RD led is green, and if I hook it up to the laptop, the TD led is red. I'm wondering if the RD should be red too (need an inverting buffer?).
Click to expand...

I'm not sure if inverting the RS-232 signal from high to low would do the trick or not. What is needed is to change that line from input to output (or is that saying the same thing?)...I'm so confused...

--T
 
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