Serial console problems on 11/34

[Tony Duell]

> 
> I get the following prompt:
> 
> XXXXXX XXXXXX XXXXXX XXXXXX (where XXXXXX is the register values)
> $ 
> 
> It's just that I can't respond to it. "L" for example is not echoed on the
> terminal when I press a key.

OK, your machine is basically working. The CPU seems to be running the 
console firmware, it can talk to the transmit half of the DL11. You've 
also not used a straight-through RS232 cable -- the output of the PDP11 
is certainly going to the input of the terminal.

Here's how I'd attack this problem (being a hardware hacker...)

1) Make sure the terminal is sending something. Put a breakout box 
between the terminal and the PDP and press keys. Check you get some 
indication on the breakout box LEDs that the TxD line from the terminal 
is changing state.

2) Grab the printset for the DL11 and look at the output of the buffer 
chip (probably a 1489) that handles the RxD line. Put a logic probe on 
the output of that buffer, again prsss keys on the terminal and chack 
that pin changes state (if not, suspect the buffer chip, they do fail...)

3) Now put the logic probe on the serial input pin of the UART and again 
press keys. If there are no transitions here, maybe you've forgotten the 
jumper wire in the cable connector that links the output of the RS232 
receiver (or the current loop receiver) to the UART.

4) If serial data is getting to the UART, maybe the Rx Clock is missing. 
Look at the appropriate pin of the UART chip with the logic probe to 
ensure it's clocking. If you have a 'scope, make sure the frequency is 
right too (16 times the baud rate).

-tony