Very cool Steve. For M100 CP/M we can use this for external 80x24 video
keeping the RS-232 port free for TPDD which is used for migrating files
from the net.
Philip
On 6/02/2020 1:58 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
