30 Jan
2003
30 Jan
'03
1:11 p.m.
From: Ethan Dicks <erd_6502(a)yahoo.com>
As to Will's original question, I myself have wondered what it
would take to design/build a compatible device.
...
One thing that has been slowing me down is
deciding how to attach a modern device to an -8/L or -8/i -
I would recommend getting the DEC compatable cards for Dougless
Electronics to plug into the 8/I and wiring them to another circuit card.
With a bank of transistors you can convert from the negative bus to TTL and
put a small FPGA/CPLD on the board to do all the work. Attach to that
your storage of choice and your all set. A fast microcontroller might
also be an option and might be needed if you want to do things like IDE/CF
to emulate DF32/RF08. Might need to be a little careful that modern fast
logic doesn't see/make glitches on the bus.
For my online PDP-8/E the board I made is a Xilinx CPLD (they have cheap/free
tools and I have the pay stuff at work) which emulated the front panel
and also was a single cycle data break master for data transfers. Most
of the 8/I peripherals were 3 cycle that wouldn't be too hard to do.
I used a little adapter board to convert the PLCC to a PGA and then
wirewrapped. I have also seen a bunch of ads for real cheap PCB prototypes
if you have confidence in your design.
Anybody who wants my code can have it but it is ugly. I first tried
another chip and coded it in that language but the tools were too bad so
switched to Xilinx and Abel.
David Gesswein
http://www.pdp8.net/ -- Run an old computer with blinkenlights.