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Thread: 8085 SBC Monitor: It Begins!

  1. #1
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    Default 8085 SBC Monitor: It Begins!

    I finally finished interfacing a Zilog Z8530 Serial Comms Controller with my 8085 SBC last night. I finished debugging the hardware (switched Tx and Rx pins between the SCC and MAX232 shifter...real pain to debug!) and wrote a bit of test code for it. The first bit of code simply took chars received from the SCC and displayed them on the DL-2416 ASCII LED display I'd incorporated with the prototype. The next bit is the start of a ROM monitor. So far, I've got memory dump mostly implemented, though it currently starts at 0x1000 on reset and increments by 0x0F every time you call the command. Of course, I'll implement memory dump at a starting location and over a range, but for now I have this:

    monitordump-scaled.jpg

    Here you can see the signon message and a few lines of memory dump (starting at 0x1000, 16 bytes per line) displayed on my Compaq Portable/386, which serves as my terminal and EPROM burner. The monitor is currently running at 9600 bps.

    Eventually, there will be an etched PCB designed with a Z8530 SCC and a Z8536 CIO (Counter I/O), in PLCC packages, on a single stacking board. Full write-up to follow!

  2. #2
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    Nice work so far!
    Torfinn

  3. #3
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    After working out the details of the output routine, I wrote another routine to convert ASCII from the console into hex nybbles, and a routine that gets two hex chars from the console and converts them into a byte. This utility, combined with the JMPOUT output routine, allowed me to add an output command to my monitor:

    v2outputtest-scaled.jpg

    Right now, the command for output is "C" (will be changed to "O") followed by the port address and the data byte to output. The monitor's input routine currently adds the spaces a la the NorthStar monitor: you type "C", and a space is automatically inserted, and the monitor is ready for the next bit of input. After C 03 38, C 02 30, C 01 38, C 00 35 the debug display contains the following:

    8085output-scaled.jpg

    Success! Next, I'll add a byte-wide input port, probably using a 74LS244 or 245. Then I'll have something to test a port input routine with. Here's a picture of the prototype so far, showing the SCC, DL2416, 74LS138 for I/O space partitioning, 74LS04 to invert a signal for the display, MAX232 and a 4.9152 MHz oscillator for the SCC's baudrate clock. Most of the connections are wire-wrapped, except power and those to/from the MAX232 and the 10-pin header for the serial port.

    12sep2011dev-scaled.jpg

  4. #4
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  5. #5

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    Nice

  6. #6

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    Awesome! I love seeing and reading about other people's homebrew computers. Once I get a little farther on mine, I'll post it. Keep hacking and keep up the good work!

  7. #7
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    Thanks! I need to revisit this project, I have ideas for expansion and improvement that I think other people would be interested in building!

  8. #8

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    Can't wait to see your other ideas. The sad thing about mine is, that I've spent a LOT of money on parts, which could have easily paid for a nice, modern computer. But I'm learning, so it's worth it lol.

  9. #9
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    This was essentially a junk bin build -- I found an 8085 on an old AT&T telco board I was given during middle school, and by college I actually had enough experience/knowledge and free time to design something to use it! The PC boards, in prototype quantity, are the most expensive bits.

  10. #10

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    I have made a similar device based on a NEC 8080, scavenged parts during some years and finally found a suitable keyboard on eBay and made a replica of the NEC TK-80 trainer which was in one of my old schoolbooks.
    Always wondered what it would be like to use that machine. It has no monitor or such just hex keyboard entry and some 7 segment displays. I did manage to connect a modern RGB OLED display to the 8255 PPI and even port a Breakout game on it. Now it is sitting nicely in my 'trophy showcase'

    BTW my only 80(C)85 machine is a portable Casio FP-200

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