a classiccmp electronics project? - test-drb@ccmp.vtda.org

30 Jul 2004

...
 From: ard(a)p850ug1.demon.co.uk

 Tony wrote...
  Yes, modern SRAM is fast enough. But that's
'easy' in theory. Firstly you
 have to have some way of switching the SRAM between the device and the
 loader  Dual port SRAM is one answer. Or, I'm not sure what the power on test
in 
Sure, but have you looked at the price :-) 
Hi
 You use single port RAM with an output buffer ( could even be
a 7404 but it would most likely need a 3state control, '240 or '244 ).
You hold the machine in reset while you transfer data to the
RAM ( It doen't make much sense to do it on the fly with
the machine actually running ).
This isn't much more complicated than a memory board.
Dwight

...

  microcode does on the MX's, but my guess is
it doesn't touch the add-on
 microcode. The loader roms probably aren't touched either until called from
 the front panel. If the RPL stuff is turned on, it may though. I think the 
OK. I was thinking about the microcode ROMs in an HP9810 (somethign that 
_I_ am working on, and those are most certainly 'hit' as soon as INIT is 
deaseserted and the microocde program counter starts to change. I prefer 
to think of general-purpose solutions (i.e. somethign that will replace 
every 256*4 ROM), rather than soemthing that works only in specific 
machines under specific circumstances.

-tony