While an old Creed 75R proved adequate for listings etc, it
mas hardly suitable for letters and reports. Therefore, seeing
an ad. in Wireless World for IBM printers, i trekked to Essex
and bought myself an old 3962 Terminal printer. I also received
with it some suggestions on interfacing. These struck me as
somewhat crude and rather incomplete, having no software with
them. So, I set about designing my own.
Firstly, the hardware. Octal buffers to switch between
characters and control and then 7-way Darlington drivers
(ULN2003) to drive the operating coils. The timing contacts on
my machine where not all c/o as per the handouts. So, they are
just inverted as necessary and added to ARDY to generate a Busy
signal. An enable signal for the octal buffers is derived and
switched with bit 7 to determine control or character. The TTL
is powered from the Nascom and the coils from a simple 48V ps.
The worst part is stripping out and identifying all the wiring,
then stuffing it back neatly.
Secondly, the software driver. (The nut behind the wheel).
This is based on a look up table. Nulls are returned unused. A
linefeed after a CR is also thrown away. Full stops are sent
either case to improve speed. Character case is compared with
the printer and any appropriate change sent. Finally, a routine
for printer busy is ended with a short delay which I found
necessary to ensure complete settling after Busy is finished.