one more question about pdp8/e console switches behaviour

From: Pete Turnbull <>
Date: Thu Nov 11 02:08:01 2004

On Nov 11 2004, 8:32, Gooijen H wrote:
> Hello all,
> I have the pdp8/e *including* the console running on the Core
> 6809 Board (plus one I/O Board)!

Nice! I look forward to seeing this.

> If the HALT (or SING STEP) switch is down, you can use the EXAM
> and DEP momentary switches. If I press EXAM, I want to see the
> 12-bit word contents of the address currently on display in the
> top row (memory address) of the console.
> That 12-bit word is displayed on the 12 lights below the memory
> address lights. Is it correct that the position of the selector
> switch (the rotary knob) must be on "AC" to see the contents of
> the active address? Or is its position not relevant while HALT
> (or SING STEP) is active which seems odd to me because you want
> to be able to see more than just the AC when you HALTed the CPU?

The position is always relevant, but you don't set it to AC. You set
it to MD (Memory Data). And when you press EXAM (or DEP), the address
displayed on the upper row will increment (but the data displayed will
remain the same, the data for the address that was current when you
pressed EXAM/DEP).

> The answer seems easy, I just want to hear confirmation.
> The current implementation shows the contents briefly after I
> pressed EXAM *and* the knob is on "AC". Just *very briefly*,
> then the simulation shows the actual AC content again.

It shouldn't do that.

> So, on a real pdp8/e I assume that when the knob is on "AC" you
> see the contents of AC when HALT is active?

Yes, without any glitches from the data. But only if the rotary knob
is turned to the AC position, otherwise you see whatever you've
selected (STATE, STATUS, AC, MD, MQ, BUS).

> In that case, after the user pushed EXAM once (and the memory
> contents is displayed as I described above), how does he get to
> see contents of the "AC" again?
> Hope I made myself clear why I asked the question ...
> TIA,
> - Henk, PA8PDP.

Pete						Peter Turnbull
						Network Manager
						University of York
Received on Thu Nov 11 2004 - 02:08:01 GMT

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