22 Apr
2024
22 Apr
'24
1:52 p.m.
On Mon, Apr 22, 2024 at 2:30 PM Paul Koning via cctalk
<cctalk(a)classiccmp.org> wrote:
Anyway, I would think such a small microprocessor
could emulate a PDP-11 just fine, and probably fast enough. The issue isn't so much
the instruction set emulation but rather the electrical interface. That's what would
be needed to be a drop-in replacement. Ignoring the voltage levels, there's the
matter of implementing whatever the bus protocols are.
Emulating an F-11 chip or a J-11 chip is certainly possible with a
modern MCU, just need TTL-friendly I/O. F-11 is 40-pins (and can have
additional instructions added by adding microcode ROMs next to the
CPU) and the J-11 is 64 pins on a fat chip carrier.
Possibly an RP2040 (the engine in the Raspberry Pico)
would serve for this, with the PIO engines providing help with the low level signaling.
Sounds like a fun exercise for the student.
Could be a good start but would still need level shifters.
J-11 runs at 15-18Mhz for an idea on how fast the bus implementation has to be.
-ethan