26 Mar
1998
26 Mar
'98
5:44 p.m.
On Thu, 26 Mar 1998, Tony Duell wrote:
At a guess, the 50 pin ones are parallel I/O ports and
the 26 pin one is a
serial port (you mentioned the 8251, which is a USART chip). Try tracing
grounds and then signals (maybe to 1488's and 1489's)- you may find that a
straight IDC cable will link the 26 pin connector to a 25 pin serial port.
Don't plug it in without checking, though.
Your guesses seem correct about the function of the connectors, but I'm
not so sure about the mapping of the 26-pin connector -- they seem like
they might be reversed from what I would expect. Here are a few I buzzed:
26 - gnd
25 - transistor Q1
24 - 1488.1 (Vee)
14 - 1489.4 (2A)
13 - 1488.2 (1A), 1489.14 (Vcc)
5 - 1488.6 (2Y)
4 - N/C
3 - 1489.13 (4A)
2 - N/C
This means very little to me, other than I vaguely recall that the 1488
and 1489 are drivers (and I found a pin-out for them on the web), and I
expect ground, TX, and RX on the first three pins.
-- Doug