PDP 11/73 is ALIVE!

Well, except for s/BME/BNE/ on the third line (address 2004) and s/.R4/,R4/ on the twelfth (address 2034), this looks not entirely unreasonable. With those fixes, and changing the labels, the contents given match what my assembler produces for that code (except for the .end line; I don't know why your listing shows a value there). (I had to change the labels because my assembler doesn't accept labels beginning with a digit, and it was easier to change the labels than to change the assembler.) So it had sent the command to the tape but was sitting in the spin loop at locations 2026 and 2032, waiting for the ack. Given how small this is, and the control structure of the code, it appears to be expecting the device at 172552 to DMA some boot code into low memory; when this is done, as signaled by finding 122204 in what I assume is the device's CSR, it jumps to it with the CLR PC. It might be instructive to clear low memory first, then run the above code, and see if low memory has changed. For example, 001764 012700 b: mov #b,r0 001766 001764 001770 012701 mov #b/2,r1 001772 000772 001774 005040 x: clr -(r0) 001776 077102 sob r1,x the rest of the code as above, and then use 1764G. When you break it, examine low memory (type 0/ and just hit return a bunch of times). If low memory isn't all 0, _something_ has changed it, and if you send me the contents (a capture of the output when you hit return until you find a bunch of all-0 memory locations) I can disassemble it for you. Not that that will _necessarily_ help, but if the disassembly makes sense, there is an excellent chance the hardware is connected correctly. Order of cards matters in two ways: (1) the bus slots have chained signals, and if you have any empty slots between the CPU and the last card, you need to put jumper cards in them to pass along the chained signals; and (2) card order determines priority for something - I forget whether it's equal-priority interrupts or DMA bus grants or what, but you want the cards for which timing is most important to be closest to the CPU. /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B