yah interesting. Almost the same approach. I think it is wise to take the TTL signal from the output of the schmidt trigger buffer, rather than from the CPU itself. So in M100 use case that would be inverted TTL. But overall, the same.
On Wed, Feb 5, 2020 at 9:47 AM Kurt McCullum <ku...@fastmail.com> wrote: > 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. > > [image: 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 > > >
