exactly the motivation ;) BTW I have my VT100 emulator board running. Tonight I hope to fire characters at it using this mod.
On Wed, Feb 5, 2020 at 11:55 AM Mike Stein <mhs.st...@gmail.com> wrote: > Neat; will have to check it out. > > Sounds like the perfect answer to redirecting the video to an external > terminal/display while leaving the RS-232 port available. > > And if you're going to use 'real' RS-232 you'll probably have to invert it > anyway. > > m > > > ----- Original Message ----- > *From:* Stephen Adolph <twospru...@gmail.com> > *To:* m...@bitchin100.com > *Sent:* Wednesday, February 05, 2020 10:27 AM > *Subject:* Re: [M100] sending fast data using modified cassette port > > 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 >> >> >>
