18 Mar
1999
18 Mar
'99
7:41 p.m.
On Mar 18, 21:37, Tony Duell wrote:
It has a redefinable character set (the bitmaps are in
RAM).
Only for the characters 128...255. The lower set is always in ROM.
It has a
real serial port, which is also used for the cassette system
Mk.1 versions have a hardware bug which gives the RS232 transmit line
incorrect polarity. All standard versions have a bug in the monitor
routines, which cause the baud rate and serial/cassette switch to be rset
every time the keyboard is scanned. (I have a fix for that).
(most of the
cassette I/O is done in hardware which couples to the UART chip).
That was one of the nice things -- quite a good cassette system, with motor
control.
It has
a parallel port (centronics printer or user I/O IIRC). The keyboard isn't
too bad.
Except it's polled by a very inefficient routine, which makes it a bit
slow. But it's good quality otherwise; it uses the same keyswitches as some
DEC terminals, and has a full ASCII keyboard, with a numeric pad, and a few
extra keys, so it's easy to generate all 256 character codes.
It also had pretty comprehensive Technical and Software manuals. I still
use mine.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York