Advice needed: Entry point into things PDP-8

[Paul Anderson]

Hi Carlos,

With the cost of PDP-8 parts and the need for maintenance and repair, if
you can find an emulator that will do what you want, go for it.

Paul

On Mon, Oct 22, 2018 at 10:39 PM Carlos E Murillo-Sanchez via cctalk <
cctalk at classiccmp.org> wrote:

> Greetings all...
>
> I have been pondering something and would love to receive feedback from
> you.  The thing
> is, I would like to have something pdp8-ish that would allow me to play
> a little bit
> with the programming languages that were available for these machines,
> FORTRAN 4K and
> FORTRAN IV in particular.  Now,  I would love to be able to time some
> FORTRAN jobs just
> to get an idea about what it was like back then.  I am aware of PiDP-8,
> simh, as well as
> SBC6120, SBC6120RBC.
>
> I happen to have three VT78 cpu boards (sans the RAM board) and two
> vt278 cpu boards.
> All were in rather sorry condition; I picked them up from a junk pile
> that was stacked
> several feet high and in which the contents were mostly random. Thus,
> the VT78 boards'
> components were scratched and in fact two of them are missing the
> control panel ROM chip.
> Otherwise they are complete, but I am missing the RAM boards.  The VT278
> boards
> were further abused by someone who yanked out the oscillators and a few
> TTL chips,
> damaging several traces, which I have now repaired.  Alas, only one of
> them has the
> HM6120 cpu chip, and I do not know if it is good or not. Both are
> missing the SMC5037
> CRT generator chip.  Other than that, they are complete.
>
> So, now that we all know what I have, let me say out loud what I've been
> thinking:
>
> If I try to build actual hardware:
>
> I've read that the VT278 has serious software compatibility issues with
> older software
> due to the use of the HM6121 I/O chip.  So even if I get an adequate
> keyboard, buy the
> CRT chip and manage to use it to drive a monitor, I would need an
> original floppy drive
> system and media, because I do not have the DP278 serial comms board
> that would allow me
> to send the VT278 a program to run;
>
> For the VT78, I would need to hack a memory board, and, since it can be
> coaxed to accept
> a program to run if it is fooled into thinking that it is loading a
> program from an
> MR78/paper tape, perhaps I could make it boot something.  I would need
> to wire-up
> and arduino or something like it to translate the keyboard and display
> terminal
> chatter in the serial console into something usable.  But, that's three
> hardware
> projects (memory board, MR78-like contraption, microcontrolled serial
> console
> translator)...
>
> The last hardware option is to go and make an SBC6120RBC;  I would need
> to buy
> programmers for the GAL/PAL devices, and I've heard that not all
> programmers can deal
> with the kind of chips used in it.  And, if it turns out that the HM6120
> chip that I
> have is bad, I would have to hunt down one of those rare beasts.. It
> would be awesome, though,
> to have an SBC6120RBC up and running, and be able to time actual
> hardware running
> FORTRAN.
>
> And then comes the emulation option, with the PiDP-8.  I have to say
> that the emulation
> of the blinkenlights is very, very attractive to me, and this option is
> a no-brainer
> hardware-wise.
>
> So...  am I missing something in my estimation of the effort involved in
> these options?
>
> What would _you_ do?
>
> Carlos.
>
>