Time scales of a PDP-11/34 - 200 ms

Parent Category: Articles Category: Time scales of a PDP-11/34 Written by Administrator

200 milliseconds - the CPU starts up after Power-ON

In a time window of 0.2 seconds, you see how the CPU begins to run after the reset logic has processed the signals of the power supply:

la shot 200ms

Signals

Relevant signals here are:

ACLO: a High level means "AC line power is unreliable".

DCLO:  a High means: The main +5V logic supply voltage is unreliable.

PROCINIT: this signal is inverted, a High means: CPU is held in Reset, CPU clock is stopped.

What you see

  1. After power is switched ON, all signals are undefined at first. The LA shows them as Low levels.
  2. At the "T" marker, DCLO and ACLO from the power supply get valid and indicate a "Power failure".
    The micro program counter MPC is initialized to 001, which is the start of the power-up micro program.
    All other signals show constant nonsense data.
  3. After Power has stabilized, DCLO goes Low ("A" marker").
  4. 120 milliseconds later, the PROC INIT signals goes inactive (marker "B").
  5. The CPU begins to run. You see all other signals begin to oscillate so fast, that no signal traces can be distinguished at 200ms resolution.