Do-It-Yourself PDP-11 help!

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Feb 15 19:25:20 2005

> a Fourth Generation Systems memory board, with 18 41256s on it (512kwords?)

No. 256K 18 bit locations (i.e. 16 bit words with parity for each byte).
So 256kW

> The little front panel has a key switch that switches the mains on and
> off, a reset button with a "DC ok" LED, a Run/Halt switch which is
> broken, and a three-position switch marked "L.T.C. on/off". With this
> switch up, the LED above it lights up. "Local Terminal Console" is my
> best guess so far.

Almost certainly 'Line Time Clock'. The mains-frequency interrupt signal.
For some unknown reason this was controlled by software on Unibus systems
(a bit in an I/O device register), but by a swtich on Q-bus machines.

-tony
Received on Tue Feb 15 2005 - 19:25:20 GMT