| MC6800 single-board computer [message #9694] |
Fri, 28 January 2022 14:19  |
gbm
Messages: 34
Registered: January 2018
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First, this topic is about the real, old, good MC6800, not about modern MC6809/HD6309. ;)
There are almost no contemporary designs based on the MC6800. Some time ago I found a bunch of cute ceramic-case chips from MC6800 family. I thought it would be funny to see all these chips alive, so I decided to design a showcase board. The board will accommodate MC6800 or MC6802. There will be one visible modern component: the BluePill board, serving as the reset and clock for the MC6800 generator and USB-UART bridge. The board will contain two MC6810 RAMs, MC6821 PIA, MC6850 ACIA and 28C256 EEPROM (on-board programmable) and a single 7400 for glue logic. The BluePill will provide USB connection for MC6850 and periodic timer interrupt via PIA CA1 input. Its firmware will allow to select the target (6800 or 6802) and to set the MC6800 clock frequency, timer interrupt period and PIA buffers direction.
The PIA ports will be buffered to enable direct connection of a multiplexed LED display. With some effort it will also be possible to support a 3x8 matrix keyboard together with an 8-digit display.
Attached is the planned schematic - feel free to comment on it; I plan to order the boards within 3 weeks.
The board size is 94x94mm (3.7 x 3.7 in).
There is an optional clock buffer using 74xx2G04, although from my experience it will not be needed - the MC6800 is quite happy with 3.3 V open drain clock signals pulled high with resistors.
All the passive components will be SMT 0603 size; they will be placed on the bottom side to avoid spoiling the old-fashioned chips' appearance.
The 7400 may be substituted with 74xx1G08+74xx1G00 occupying the same space on the PCB.
If there is any interest in this board, I may order a few more and populate them with the SMD components. The firmware for BluePill will be made available, at least in .hex format.
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Attachment: M6800-1.png
(Size: 76.78KB, Downloaded 1010 times)
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| Re: MC6800 single-board computer [message #9704 is a reply to message #9694] |
Sun, 30 January 2022 12:43  |
phil_g
Messages: 32
Registered: November 2020
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Watching this with interest, one of my current ongoing projects is a SWTPC6800 reproduction, it uses a Mike Lee 6802 PCB with 40k of static and switchable Mikbug, SWTbug and my own variation of a Mikbug-compatible monitor originally by Ed Smith. The monitor has a command to copy Robert Uiterwyk's TSC Microbasic to ram as its not rommable code but is interesting as it uses BCD maths. I've other homebrew 6802 computers too, some are on my Yooch channel PHILG2864 so I'm a genuine fan, looking forward to seeing your results!
Cheers
Phil
PS its just occurred to me.... gbm? is that you, Mike? 
[Updated on: Mon, 31 January 2022 15:43] Report message to a moderator |
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