Interesting Steve, As I was looking at that I couldn't help but think of the TTL output that the NEC8201 has available on Pin 1 of the cassette port. Looks like you may achieved something very similar.
For input you could always look to the BCR port. The two could be used in conjunction to create a TTL i/o pair. Kurt On Wed, Feb 5, 2020, at 4:58 AM, Stephen Adolph wrote: > I've been toying with using the cassette port to send serial data, for use > with an external device that only takes input data. Kinda the opposite of the > BCR port. > > The point being - to save the RS-232 port for bidirectional comms. > > After some experiments, I think it is quite useful. I have been able to > demonstrate an absolute maximum speed of ~100kbits/sec (which isn't all that > useful given the typical serial port speeds) and a more useful 57600 > kbits/sec. > > Quite respectable! > > To use this routine, you need to make a small change to the hardware. There > are two unused pins on the cassette port (suggest using pin 7). > Install a single lead from pin 7 to pin 12 of M34. This wire bypasses the > analog filter used by the cassette circuit, and allows the direct output of > high speed signals. > Connection to an external device needs only 2 wires from the cassette port - > ground and Tx data. > > cassette hack.png > > A demonstration routine is attached that just loops and sends the same > character out the cassette port is attached. At the core it is a very short > routine. > Comments welcome. cheers Steve > > > *Attachments:* > * cassette hack.png > * sndcas_57600.asm
