Subj : Re: BBSing on CP/M
To   : poindexter FORTRAN
From : Dr. What
Date : Thu Sep 09 2021 08:24:00

-=> poindexter FORTRAN wrote to Ron Lauzon <=-

 pF> I wonder what kind of UART they used on old CP/M boxes? With DOS boxes
 pF> they originally had a 8250 UART chip that wouldn't support speeds over
 pF> 9600 (if you were lucky). 16450 and 16550 UARTs added an on-chip buffer
 pF> that allowed bits to "back up", so to speak, and higher rates were
 pF> possible.

Based on the Kaypro manuals that I've been able to locate, they didn't have a
modern-type UART.

The schmatic lists WD1943/SMC8116 and 3884/0 SIO chips.

I know in my RC2014, they use a Z80 SIO/2 chip with a 74HCT04 and 74LS138 for
providing 2 serial ports.  But that system supports speeds up to 115,200 BPS.

Like I said, it looks like my Kaypro can handle much higher speeds.  But it's
I/O for the other things that causes the problems.  It's like there's no buffer
on the serial port at all.  Get the character when it's there because it will
be overwritten soon.


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