PDP-8 CPU question

[Ethan Dicks]

On 6/18/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> > I think in this case, the JSR/ROM issue is moot... doesn't the M8317
> > 'toggle' the boot into low core?  I didn't think M8317 PROMs were
> > memory mapped.
> 
> If that's the diode matrix boot ROM then yes it does. The 'SW' switch on
> the panel starts the process, the ROM board then acts like a front panel
> (does the same things to the Omnibus signals) to copy the bootstrap into
> core. IIRC one of the rows of diodes defines the start address (the board
> effectively does a load-address operation with those diodes acting like
> the panel switches).

What I am talking about are the pair of bi-polar PROMs that are on the
M8317 board that is pretty much standard with the PDP-8/a... it has a
bank of DIP switches to select the boot device (out of 4 possible),
and _that_ bootstrap is toggles into low core when you hit the SW/Boot
switch.  It works like the diode-matrix board, but is integral to the
multi-function board.

I am _not_ talking about the 13-bit RAM/EPROM board that was far less common.

-ethan