Thinking about PDP11 PC05 Emulation

[Jay Jaeger]

On 3/11/2019 5:15 PM, Brent Hilpert via cctalk wrote:
> On 2019-Mar-11, at 2:37 PM, allison via cctech wrote:
>> On 03/11/2019 02:11 PM, Jay Jaeger via cctech wrote:
>>> 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).
> 
> . . . 
> 
>>> BUT - it also occurs to me someone may have already done something like
>>> this?  Any leads / ideas?
> 
> . . .
>> To do the data you need 8 bits but you can bit bang them out using two
>> lines on a nano to
>> a 74ls164.  The rest you use transistors (open collector) to do high
>> current (though 5V,
>> 1K pullup is only 5ma) and I'd do that to make the IO more rugged and
>> ESD proof.  That
>> covers the strobes and control lines.  Just using two lines to get the 8
>> data lines via a 164
>> frees enogh pins for there to be surplus IO lines.
> 
> . . .
> 
> I've used an RPi for tasks like this in much the same way as Allison is describing -
> reduce the number of I/O pins needed on the modern microcontroller by serialising
> the legacy-device parallel data lines with a simple TTL shift register.
> 2-4 pins (CLK,LATCH,DIN,DOUT, depending on app) from the microcontroller
> can be translated to 8,16,32 or as many data lines as you need.
> 
> 

I had thought about an RPi as well.  But the RPi is it is 3.3v,
requiring additional hardware, which I'd like to avoid.  A 5V Arduino
(or a PIC, for that matter) should be able to drive the interface card's
inputs on its own.