Muntz65 and Muntz80, two similarly minimal computers
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Bill Shen
Dec 10, 2023, 8:32:26 PM12/10/23
to retro-comp
A couple projects I'm currently working on are Muntz65 and Muntz80, named after "Madman" Muntz for brutal simplifications. Both are similar bare-bone designs based on a 22V10 as the serial port and glue logic. The designs are simple, just CPU. RAM and 22V10, but fast with 25.175MHz CPU clock. Serial port is 115200, bit-bang transmit and receive. My goal is to put both designs on a pc board so you can have Muntz80 with Z80 and 22V10 programmed for Z80 or 6502 with 22V10 programmed for 6502. They meant to be cheap, easy to build, and hopefully fun to play with.
Muntz65 is a week older, on-going discussion here, and homepage here.
Working on Muntz80 right now...
Bill Shen
Dec 11, 2023, 7:29:24 PM12/11/23
to retro-comp
I've changed Muntz80 name to barebone80 or BB80 which is a more descriptive name. It is working now and has a homepage for the design here.
Even though it looks very much like the 6502 version and use a 22V10 for bootstrap ROM and bit-bang transmitter, Z80 version needs an additional page register to swap out the ROM in zero page and replace it with RAM. That process is more complicated so I was rather pleased that I'm able to do it with a 22V10. I wrote down the details in Theory of Operation section of BB80 homepage for my own benefit because I just know I won't remember it a month from now.
I plan to build a PC board with overlapping sockets for Z80, 6502, and an uncommitted 40-pin DIP so the same board can be a single board computer hosting one processor (6502, Z80, or another 40-pin retro processor) , a processor-specific 22V10, and RAM.
Bill
Even though it looks very much like the 6502 version and use a 22V10 for bootstrap ROM and bit-bang transmitter, Z80 version needs an additional page register to swap out the ROM in zero page and replace it with RAM. That process is more complicated so I was rather pleased that I'm able to do it with a 22V10. I wrote down the details in Theory of Operation section of BB80 homepage for my own benefit because I just know I won't remember it a month from now.
I plan to build a PC board with overlapping sockets for Z80, 6502, and an uncommitted 40-pin DIP so the same board can be a single board computer hosting one processor (6502, Z80, or another 40-pin retro processor) , a processor-specific 22V10, and RAM.
Bill
Bill Shen
Dec 12, 2023, 2:16:55 PM12/12/23
to retro-comp
Even though BB80 has no mass storage, it is still possible to run a CP/M application in RAM. A program of interest is zexall.com which is useful to test the 25MHz Z80. To that end, CP/M22 is ported to BB80 by replacing the console I/O with bit-bang transmit/receive routines. CPM22 is loaded at high end of RAM; zexall.com is loaded in RAM starting at location $100 and the BDOS jump address initialized at $5. This is zexall running in BB80. It finished the test in 31 minutes
Bill
Bill
Bill Shen
Dec 15, 2023, 11:15:01 AM12/15/23
to retro-comp
BB80 has bit-bang serial transmit and receive like SC114, so I patched SC monitor to run on BB80. The advantage is having BASIC that comes with SCMonitor. This is the Mandelbrot benchmark running in SCMonitor's BASIC.
Bill
Bill
Bill Shen
Dec 27, 2023, 11:09:24 AM12/27/23
to retro-comp
Since Z80 bit-bang the serial transmitter, it is possible to bit-bang WS2812 LED in parallel. WS2812 needs much higher data rate, so the high frequency WS2812 output may cause little or no spurious data to the serial port. Conversely, the normal serial traffic may not generate valid data write to WS2812. The biggest challenge is 25MHz Z80 is just not fast enough to drive WS2812; the "out (SerTx),a" instruction required to bit-bang the serial transmitter already uses 11 clocks which is 436nS at 25.175MHz and that's already the entire budget of pulse width for WS2812.
Interestingly, 3 consecutive "out (SerTx),a" instructions at 25.175MHz is very close to WS2812's 800KHz pulse code modulation where "one-high-two-low" is a '0' and "two-high-one-low" is a "1". So if we execute 24 triplets of "out (SerTx),a", it will have the correct timing to drive a WS2812 with the 3-byte color data. Now all we need is a self-modifying program that alters the instructions according to desired color values.
To drive a panel of 8x8 WS2812, the attached program has 1536 triplets of "out (SerTx),a" (64LED x 3 colors/LED x 8 bit/color = 1536) that are first initialized according to the desired color pattern (a tree with white star at its tip) and then jump to execute the modified program.
Bill
Interestingly, 3 consecutive "out (SerTx),a" instructions at 25.175MHz is very close to WS2812's 800KHz pulse code modulation where "one-high-two-low" is a '0' and "two-high-one-low" is a "1". So if we execute 24 triplets of "out (SerTx),a", it will have the correct timing to drive a WS2812 with the 3-byte color data. Now all we need is a self-modifying program that alters the instructions according to desired color values.
To drive a panel of 8x8 WS2812, the attached program has 1536 triplets of "out (SerTx),a" (64LED x 3 colors/LED x 8 bit/color = 1536) that are first initialized according to the desired color pattern (a tree with white star at its tip) and then jump to execute the modified program.
Bill
Bill Shen
Jan 15, 2024, 6:48:02 PM1/15/24
to retro-comp
Combined Muntz65 and Muntz80 into one pc board and named it BB6580 for barebone 6502/Z80. I think it may be useful as a tester to check out CPU/RAM/22V10 acquired over eBay. In fact, other than W65C02, all parts in these pictures were eBay items. eBay's 6502 is only capable of 4MHz; you'll need to buy W65C02 from Mouser or DigiKey to run it at 25.175MHz.
Homepage under construction is here.
https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:bb6580:bb6580r0home
Bill
Homepage under construction is here.
https://www.retrobrewcomputers.org/doku.php?id=builderpages:plasmo:bb6580:bb6580r0home
Bill
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