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.