Taken: AT 286 motherboard with mathco

Pete Turnbull 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
						Network Manager
						University of York



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