Just pondering the 150 pair cable connecting the console on my 1970's era
PBX to the main cabinet, and after a look through the schematics, I think it
would be possible to reduce this whole deal to a piece of category 5, using
a PIC.

There are 180 12v lamps on the console, 20 spst switches, and a 3x4 key
matrix -- 180 inputs for the console and 27 outputs.

What would be the best way to get all this data onto 1 twisted pair that
could be around 1000 feet long (What serial protocol? RS-422?), with a
reasonable refresh rate that would not miss any button presses?

What would be the best way to control 180 outputs with a PIC, and drive 180
'common anode' 12v lamps? My PBX uses 3 8" x 9" boards covered with a 4x10
grid of transistors and resistors.

I would actually have to input 180 12v signals at the PBX end, send the data
over the serial link, then output to 180 12v lamps!

With the 27 switches I would have to read 27 12v signals at the console end,
send the data over the serial link, then output as 12v signals to the PBX.

The other 3 cat 5 pairs would be used for the voice link to the console.

----+                                                         +---------+
PBX |=+---------------+                     +---------------+=| Console |
    |=| PIC Interface |xxxxxxxxxxxxxxxxxxxxx| PIC Interface |=|         |
    |=+---------------+     Serial Link     +---------------+=|         |
----+                                                         +---------+

Which PIC would be the best for this application?

I am thinking that I could have a PIC controlling a fistfull of shift
registers, loading them all at once then shifting the data into the PIC for
transmission. The receiving end would do the reverse. Also, what would be
the best way to convert a 12v signal to a 5v signal suitable for use as a
TTL input, with the least amount of parts? (While simulating the load of a
'51A' (Not Amps :) telephone console lamp.)

All help is greatly appreciated,
- Keelan Lightfoot