Re: serial port under CP/M

[alex.freed.007@gmail.com]

On Jan 16, 4:45 am, Steven Hirsch <snhir...@gmail.com> wrote:
>
> The ring-buffer driver was interrupt driven and held 256 characters on the
> Apple side for programmed retrieval.  I _think_ I was able to get 9600 baud
> file transfers using that arrangement.  In terminal mode, 2400 was the limit
> without character loss.  There, you took the overhead in both directions since
> the displayed text had to go back over the interface with each character received.

I understand that the main attraction of CP/M was portability and
ideally the
programs ran on any CP/M platform. However looking (for the first
time) at
the concept of "overlays" for different computers that apparently
served as low
level device drivers it becomes clear that portability was not 100%.

PCPI card is very interesting because it's a multiprocessor system. It
may be
a good exercise to write a file transfer program with the SSC
interface running
on the 6502 side. Just like a disk driver. Serial port may be a
"character device"
but it becomes a block device for xmodem protocol. So 6502 can get a
128 bytes
block via SSC at 19200 baud  and give it back to z80 all at once.

Of course having a SIO (or a USB interface) on the z80 side takes care
of the
problem :)

-Alex.