Adding I2C Via Hardware Port?

General discussions related to the Altair 8800 Clone

Adding I2C Via Hardware Port?

Postby TimC » December 11th, 2017, 5:49 pm

Hi All,
I just got my Clone last week and it's great. My first project was to take my 1981 Hayes Chronograph request and read the time. Interpreted basic not being the fastest just barely made it at 300baud without loosing any received characters. It was fun going back to 2Mhz and it's realities. But now I want more, there is a lot of room in the big blue box.

Why not add 2 Hardware ports that translate to SCL/SDA hardware of the PIC24FJ128? I2C did not exist back then but there is no way S100 is going to happen with a PIC24. If a I2C bus was available existing compilers and assemblers would work just by sending the read or write address followed by the data bytes. Start and Stop bits would also have to be added in firmware. The Ports could look like the 2SIO ports, status/data pair or maybe status/address/data using 3 ports.

The 8080 could act as if it was controlling a fancy parallel to serial converter to produce the I2C protocol. So debugging and blink'n lights would work as they should.

We could be adding Sensors, time clock, A/D converters, I2C to parallel, Speech. Add some interesting experiments to to what this box can do.

Regards Tim C
Boston MA
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Joined: May 6th, 2017, 12:28 pm

Re: Adding I2C Via Hardware Port?

Postby AltairClone » December 13th, 2017, 11:58 am


Sounds like a good project for an assembly language program. The program could easily keep up at 9600 baud. You could develop and run under Altair DOS or CP/M, or if you really want old-school, under Altair's Programming System II.

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