SimH PDP-8 ttox device help

David Gesswein djg at
Tue Jan 20 16:01:54 CST 2015

On Sun, Jan 18, 2015 at 07:02:22PM -0500, Kyle Owen wrote:
> I wanted to extend this to a VC8-E emulator, again in the simplest way
> possible. I am sending out the X- and Y-coordinates for the point over
> TTOX0, but seem to be encountering some problems. I noticed that it likes
> to get hung up on a TSF (6411) instruction, causing it to keep looping even
> in single-step mode! Assuming everything is buffered, I would be under the
> assumption that TSF would almost always skip with a successful device send.
> I noticed David Gesswein opened up a somewhat related issue, now marked as
> closed, in October 2013.
SIMH has some delays to better match real hardware behavior. From my
memory on when I was looking at this it still doesn't instantly raise
the flag though allows much faster transfers than a real serial port. The delay is in cycles not
real time so single step still needs to execute the same number of

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