Thinking about PDP11 PC05 Emulation

[Henk Gooijen]

Hi Jay,

Have a look at www.pdp-11.nl/peripherals/tape/pc05-simh-pc.html<http://www.pdp-11.nl/peripherals/tape/pc05-simh-pc.html>

If you are interested I can tell you more …



I can read and punch tape. PC05 + interface (PIC 18F4550) connects using RX/TX to USB to PC.

Reading one character at a time works fine (speed some 20 char/sec, so-called start-stop mode).

Reading in “streaming mode” is probably some 300 char/sec, but I get unexplained “out-of-paper” state sometimes, and reading stops (of course).



To read from the PC05 reader you need IOP2, IOP4, and INT*. Maybe BUSY* is needed, not sure about that.

INITIALIZE* is good to have as well. A few other signals (for example IOP1) needs to be connected to an appropriate level. And 8 data inputs, which need a pull-up resistor. Note that the data from the reader is inverted.



To punch you only need IOP4 (IIRC) and of course 8 data outputs.

As you know, reader and punch are two completely isolated devices.



Greetz,

Henk





________________________________
Van: cctech <cctech-bounces at classiccmp.org> namens Jay Jaeger via cctech <cctech at classiccmp.org>
Verzonden: Monday, March 11, 2019 7:11:46 PM
Aan: General Discussion: On-Topic Posts
Onderwerp: Thinking about PDP11 PC05 Emulation

I have several PDP-11's in my collection (among other things), and not
enough PC05 tape readers (or enough room) to go around.  But most if not
all of my machines have M7810 PC11 interfaces, and I have one I could
move from machine to machine as needed.  Moving a PC05 around would be a
lot more work, and not every rack has room.  ;)

So, I took a look at what it might take to interface with an M7810 (or,
down the road, a PDP-8/L or PDP-12.  It looks like the emulator would
have to accept as input just 3 lines (Initialize  L, IOP2(1)/Select,
IOP4(1)/Read) [It would not need the redundant Initialize H, IOP1(1),
Qualify or Skip], and would have to drive 11 lines into the pullups on
the M7810 (8 Data lines, IO Bus INT L/Reader Done L, Outtape/Error and
RDR RUN L/RDR Busy L).

So, a total of 14 interface lines. (The 8 or 12 would take a few more
lines).

The pullups average about 470 ohms (1 is 1K, 1 is 220, the rest are
470), so at 5V the output has to sink a bit over 10ma, and all total
120ma.

An Arduino Uno with an Ethernet shield would have 20 minus 5 lines
available, in theory, but if one wants serial I/O as well for debugging,
that sucks up 2 more lines - so only 13 available.  And sinking 120ma
would be a bit much though I could likely sprinkle inputs among the
outputs to make it work so as to stay within the recommended sink
limits, and at least initially have it never run out of tape, and tie
Error down.

http://playground.arduino.cc/Main/ArduinoPinCurrentLimitations

So, I am thinking about an Arduino Mega, as it has more output groupings
to sprinkle the sink current around, and 5V interface capability, and
more pins to eventually support my PDP-8/L and PDP-12.

(I could do it with a PIC - did that for a Documation card reader to PC
interface, but I am really tired of fighting Microchip's IDE.)

BUT - it also occurs to me someone may have already done something like
this?  Any leads / ideas?

JRJ