Thread: Mk14 vdu
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Old 5th Jun 2020, 2:06 pm   #49
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
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Default Re: Mk14 vdu

You need one of the later Philips 'Computer Controlled Teletext' ICs in the SAA5240 series. Those let you read/write the memory over the I2C bus. Doing it with the older SAA50x0 series chips is a lot of work!


Yes, it's easier to simulate the I2C bus using the 8154, but that chip is getting hard to find. You can get away with a couple of diodes (to turn totem pole outputs into open collector ones) and pull up resistors. From what I remember you don't need to sense the SCL signal (just drive it) in a simple application like this so you could use a couple of the SC/MP flag outputs to drive the lines (via the diodes) and monitor SDA using the Sense B input or something like that.

At one time Philips produced a user manual for the SAA5243 which included a lot of useful information not in the data sheet. I have no idea where you'd get it now.
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