one more question about pdp8/e console switches behaviour

From: Gooijen H <>
Date: Thu Nov 11 03:05:28 2004

Thanks very much for the clear answer, Pete.
I have a webpage "in development", and hope to add a few pictures
representing the latest state of affairs. There is also a ZIP file
but it is an old version ... I will clean up the current source
(remove some debugging stuff) and make that available for download
as well. If you have a working Core Board *with* the extra 16k RAM
chip, you can run the pdp8/e simulation without the I/O Board by
just assembling the source with the "RealCons" conditional set to 0.
The wiring details (and more) are all in the source file. The link
to the page is: -- the click on [Homebrew 'PDP-11']
in the menu at the left, and on the page that opens click the link
[spin off] at the top right.

  enjoy (?),

- Henk, PA8PDP.

> -----Original Message-----
> From:
> []On Behalf Of Pete Turnbull
> Sent: donderdag 11 november 2004 9:08
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: one more question about pdp8/e console switches behaviour
> 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 - 03:05:28 GMT

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