3 Jan
2013
3 Jan
'13
9:38 p.m.
From: Michael Thompson: Wednesday, January 02, 2013 6:18 PM
With lots of help from members of this forum and other
friends I made
a high-speed paper tape reader emulator from a wire-wrapped interface
board and an Emcraft SmartFusion FPGA evaluation board. The interface
board plugs onto the Posibus interface slots in a PDP-8/L.
I loaded Focal from a BIN paper tape image into a PDP-8/L in about 2
seconds. That equates to about 3000 characters per second.
Nice! It is good to see someone actually get a PDP-8 FPGA peripheral of
this sort working. A number of folks have talked about it, but not got
anything actually running. ( know of at least one success with a PDP-11,
though.)
I will make an expanded version of the interface board
and change to
the Emcraft SOM FPGA board. That will give me enough I/O pins to
emulate just about any peripheral that you can connect to the Posibus.
That should make possible the RX08 emulation that Ethan is looking for.
That doesn't even need DMA/Data Break, just both directions of Posibus.
It would be possible to make an interface board for
the Negibus so
that the peripheral emulator could be used on earlier PDP-8 systems.
Seems like that should be straight-forward. There aren't a whole bunch
of working examples of those left, though :-(.
I like Posibus, since all the later machines (including Adrian's 8/A) have
Posibus as an available interface, and the conversion to/from Negibus
is just voltage level conversion. So if one does a Posibus peripheral,
it seems like it should be useful on 'most any PDP-8 (DECmate, not so
much). It's also dead simple, though it uses a fantastic amount of wire
and connectors, especially by today's standards.
Good work!
Vince