Taken: AT 286 motherboard with mathco
pete at dunnington.plus.com
Thu Oct 18 04:23:45 CDT 2007
On 18/10/2007 08:34, Jim Leonard wrote:
> woodelf wrote:
>>> Jim Leonard wrote:
>>> What is a "user port"?
> > Sridhar wrote:
> > I would assume something similar to the geek port on the BeBox.
> > woodelf wrote:
>> Well that would imply that you have a user wanting
>> to have the do something other than "install todays OS game".
> Neither of those responses answer the question. Tony: What is a "user
> port" as you originally referred to it, and what was it used for?
Tony actually did say what it was. He was referring to a BBC
Microcomputer, the user port on which is port B of a 2MHz 6522A VIA,
unbuffered. The signals CB1, CB2, and PB0...PB7 are brought out to the
even-numbered pins 2...20 of a 20-pin IDC header; pins 1 and 3 are
connected to the +5V supply and the rest of the pins are ground. The
timers and shift register etc in the same 6522A are also available for
user applications. Port A is buffered and used for the parallel printer
port, brought out to a 26-way header, and there's another 6522A which is
used for assorted internal I/O -- it interfaces to things like the
keyboard, the speech system, and the sound generator.
The user port was typically used for home-grown digital I/O, but some
commercial hardware used it too, eg at least one mouse, some satellite
hardware, a turtle, a robot arm, and a CNC lathe controller. I used it
to interface to a PCB tester I made to test some circuit boards I made.
Analogue input was handled by the logically-named Analogue Port, which
had a 4-channel 12-bit (but the Vref was only accurate to about 10 bits)
ADC and a few bits of digital input, so this was often used for a pair
of two-axis joysticks and their fire buttons, and for a 3D joystick for
CAD, called a BitStik.
Pete Peter Turnbull
University of York
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