Serial console problems on 11/34

Kevin Handy kth at
Thu Jun 22 11:32:24 CDT 2006

Julian Wolfe wrote:

>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.
>I'm going to try Don's tests tonight.
Could the problem be on the terminal end?

1. One thing to check for is that you have a good ground (pin 7 on the
DB25). I've had weird problems like this when the ground wire
was bad. You can also get strange things like short transmissions
look good, but long ones are messed up garbage (or vice versa).

2. Test that the terminal is actually sending the character. Short pins
two and three on the VT220 DB25 (transmit and receive pin) to create
a loopback connector, and see if what you type gets echoed back on the
screen. VT* terminals would sometimes fry the interface chips.
The VT320 could fry MicroVax II console ports when you turned the
terminal off.

3. What speed it this operating at? Sometimes the clock frequency
drifts (either, or both ends of the connection), and at higher speeds
it is enough to make things act flakey. Slower speeds aren't as badly

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