PDP-8 toggle-in diags (was Re: LET'S (old topic)/and PDP-8I code/update)

From: Ethan Dicks <ethan_dicks_at_yahoo.com>
Date: Sat Nov 27 14:42:39 1999

--- John B <dylanb_at_sympatico.ca> wrote:
> >> I am going to put up a bunch of little programs on my webpage so folks
> >> can test devices without trying to get a paper tape up...
>
> Your welcome. I think they will help a lot of people out as *most./all* of
> the 8 has to be running to get MAINDECs fed in.I will have the programs up
> on the page by Monday morning.

I look forward to it.

> I am having to restore PDP-8s *really* fast
> so I have to be able to find problems quickly.

I'm back in the swing myself... I worked on the -8/e for several hours
last night (and gave a tour to friends). I even powered up a couple of -8/L's
to see how they were (mis) behaving. One has a bad M220 card (can't load
one of the MA bits from the switch register, but incrementing the address does
work), neither works perfectly (and a third is sans core :-( )

I'm taking my Tek 465 and a TTL/CMOS IC tester out to the computer barn to
further my efforts. I built a cable with a DIP header on one end and a DIP
test clip on the other so I can quickly test M-series flip chip (at least
the simple ones like the M111, M113, M216, etc.) I have to scope out the
complicated ones like the M706/M707 I/O cards, the M220 register cards, etc.

> The most important useful <1 page programs I have had to write (over the
> past day) are:

> tty continuous output generator (character selected on SR)

Ah... I just wrote one of those... BTW, your mem test program has a typo...
the 7064 instruction (LAS) should be 7604. It threw me for a while until
I could get things sqare. I'm still re-learning machine code. I didn't
notice that 7064 _couldn't_ be the LAS instruction (wrong group).

My TTY banger has an extra feature for the -8/e - it counts characters in
the MQ register:

0200 7604 CLA OSR ; Clear AC and OR in switch register
0201 6046 TLS ; Output char and clear transmit flag
0202 6041 TSF ; Skip on TTY flag
0203 5202 JMP 0202 ; Jump back repeat TTY flag test
0204 7521 SWP ; Exchange AC and MQ
0205 7001 IAC ; Increment AC
0206 7521 SWP ; Exchange AC and MQ again
0207 5200 JMP 0200 ; Repeat entire exercise

While I'm on the topic of ONMIBUS TTY cards, does the M8650 *require*
hardware handshake?

-ethan


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Received on Sat Nov 27 1999 - 14:42:39 GMT

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