Computing > Vintage Computing

6522 + 6850 questions


Hello there,

I have a SBC with a 6522 and a 6850 connected as per image.

So the CB1 output of the 6522 act as RXClock and TXClock for the 6850 and fix the baud rate.

Reading the datasheet it seems to me that I have to use the SR Mode 4 on the 6522 to do that... Is that right ?

If Yes how should I initialize the 6522, how can I fix the baud rate and is the port B still usable as parallel port for other topics ?

Thanks for help. Regards.

Have you considered the possibility that CB1 is not the clock source but rather a clock input and shares the same clock that drives the Tx and Rx of the 6850? What are those lines connected to on the right of the schematic that we don't see?

This wire is just going to the output connector...

I am sure. The clock is generated by the 6522 CB1 pin.

      Incidentally I just became interested in those chips while troubleshooting a Keithley 705 scanner.  The MC6850 data sheet makes it look like the TX- and RX-clock pins are inputs only.  So yes, the clock must then be generated by that VIA 6522. 

      I haven't progressed on the manual of the 6522 sufficiently to be of any actual help though.  :P


After tests I can confirm that CB1 output of 6522 can act as a free run clock (into SR mode 4).



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