18 Jun
2005
18 Jun
'05
5:50 p.m.
On 6/18/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
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
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).