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68k-MBC: a 3 IC easy to build 68008 SBC running CP/M-68K

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Just4Fun:
Hi all,
I've done an easy to build SBC with a 68008 CPU.
Two HW options available: Lite and Full. Lite allows to build a 3 ICs 68008 system running CP/M-68K.

Here the 68k-MBC hardware main specs:

* 68008 CPU running at 8MHz;
* multi-boot capability;
* two main HW configuration options: Lite or Full. Lite HW configuration option allows to build a minimal 3 ICs 68008 system;
* RAM can be configured as 128/512/1024KB (1024KB supported on the Full HW configuration option only);
* optional RTC and microSD (16 HD emulation) modules (the same used in the Z80-MBC2);
* optional 16x GPIO port;
* I2C expansion port;
* 2 serial ports (Serial Port 2 supported on the Full HW configuration option only) ;
* on board RS232 drivers for both the two serial ports (Full HW configuration option only);
* serial-USB adapter support on the Serial Port 2 with independent power supply (Full HW configuration option only);
* User led and key;
* ICSP connector (for the PIC18F47Q10) for an easy firmware installation/upgrade;
* it is compatible with the uTerm (https://hackaday.io/project/165325) and uCom (https://hackaday.io/project/165709) add-on boards.
If anyone is interested all  the details are in this page.

Regards.

J4F





woofy:
Very nice.
The 68k is not a processor I've ever plated with, though I've certainly looked at it over the years. I may build one one day.
Well done.

SiliconWizard:
Interesting, and a good illustration of why Sinclair chose the 68008 for the QL.

saipan59:
Nice project! A question:
I have considered doing something similar. I see that the PIC you chose actually operates at 5V (not just "5V tolerant").
What about using an MCU that runs from 3.3V, but has "5v tolerant" GPIOs? Is it feasible? Can 3.3V signals drive an NMOS input? I looked at my favorite part, the DEC T-11, and it appears to be OK, but I haven't tried it. It seems that Vih-minimum is typically 2.0V for these older parts.

My interest would be to use a board like this, which provides a fairly high-performance MCU, with a USB programmer, and 0.1" header pins, for $13. This part is "5V tolerant", but runs at 3.3V. I have a variety of these T.I. boards on many projects.
https://www.ti.com/tool/EK-TM4C123GXL?utm_source=google&utm_medium=cpc&utm_campaign=epd-null-amcu-TM4C123g-cpc-evm-google-wwe&utm_content=TM4C123g&ds_k=tm4c123g+launchpad&DCM=yes&gclid=Cj0KCQjwvYSEBhDjARIsAJMn0ljCPUTBd_9d2xfnERhc4WU-5495RXEnB6x7ntaOwK6LhGrmqydFaA8aArt0EALw_wcB&gclsrc=aw.ds

Pete

SiliconWizard:

--- Quote from: saipan59 on April 22, 2021, 05:45:42 pm ---Nice project! A question:
I have considered doing something similar. I see that the PIC you chose actually operates at 5V (not just "5V tolerant").
What about using an MCU that runs from 3.3V, but has "5v tolerant" GPIOs? Is it feasible? Can 3.3V signals drive an NMOS input?

--- End quote ---

I just checked in the 68k datasheet:

* Safety-wise, 5-V tolerant inputs will be fine for the CPU -> MCU direction, but beware the maximum "Output Low Voltage" of a 68k is 0.5V. Check that it's ok with the MCU you select (it should be).
* For the MCU -> CPU direction, the minimum "Input High Voltage" is spec'ed at 2.0V (for Vcc = 5V), so this should work fine without any level shifter.

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