Thinking about PDP11 PC05 Emulation

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.