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SiriusHardware · 5th Jun 2020, 10:45 am

A nice idea, I bet those TT ICs were made in such large quantities that there will still be a good few around today.

It might be easier to bit-bang I2C with the 8154 ports because I2C uses the same line for data in and out, therefore you ideally need a single pin which can be both input and output.

You can simulate the open-collector nature of an I2C driver by writing a '0' to the 8154 data output latch and then control the line by changing the direction of the port pin - in output mode it will drive the SDA line low, and in input mode it will release the SDA line, which is always pulled up by a resistor, high.

5th Jun 2020, 10:45 am	#47
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,577	Re: Mk14 vdu A nice idea, I bet those TT ICs were made in such large quantities that there will still be a good few around today. It might be easier to bit-bang I2C with the 8154 ports because I2C uses the same line for data in and out, therefore you ideally need a single pin which can be both input and output. You can simulate the open-collector nature of an I2C driver by writing a '0' to the 8154 data output latch and then control the line by changing the direction of the port pin - in output mode it will drive the SDA line low, and in input mode it will release the SDA line, which is always pulled up by a resistor, high.