Hello everyone! I wrote here about my PDP-8/L a long while ago already. This is my current status: All instructions seem to work (only tried the simplest form, i.e. 5001). Core memory is mostly untested. The places I used work and retain their content. Examining and depositing works. AC, PC work: I can execute small loops using jumps and conditional skips etc. So as far as I tried it everything seems to be alright. Now I wanted to revive the teletype interface to load and try more complex programs and that is where I am stuck now: The machine has the M452, M706 and M707 modules. W076 was missing so I got a W076X from Vince that does RS232 (thanks again :-) as well. I don't have a real teletype. I used this small program to try and send characters from the switch register: 0000 7200 CLA 0001 7404 OSR 0002 6046 TLS 0003 6041 TSF 0004 5002 JMP 003 0005 5000 JMP 000 The program loops like crazy but nothing happens to the serial output. If I connect a oscilloscope to the data lines of the M707 I can see the input bits change as I push the buttons on the front panel and step trough the program. The input clock is there as well (so I assume the M452 is working) but no data stream comes out of the module. Writing this I realize that I didn't check the device selector inputs. I'll do that tomorrow. I know how to operate an oscilloscope and I have some experience with electronics but I'm not very good at reading logic and I only ever spent a couple days with this computer so I need some help here. Is there anything I have to look for especially? Next I tried receiving characters. I hook my PC up to the W076X and start sending more or less random characters. They show up on the backplane side of the W076X module and on the input of the M706 but no data comes out either. The clock input is low all the time. Two of the select bits seem to be low all the time even if I execute the following program: 0000 6032 KCC 0001 6031 KSF 0002 5001 JMP 0001 0003 6036 KRB 0004 5001 JMP 0001 Actually the above program completely hangs the computer. I stays in "run" state and on address 0002 whatever key I press. That never occured before. As you see I don't know too much about this computer. Am I using the right commands at all? I started reading the documentation and schematics (it is truly amazing how complete they are!) but I am not sure what to look for - what the signals on all the different "clear"-inputs of the M706/707 have to look like for example. Any hint is apprechiated! Sebastian PS: It's been a long day so don't mind me if I don't make too much sense...