38.4 Kbps Console

Baud rate table from the manual

The short version is that, picking up from last night, and after several cyles of removing, rewiring and replacing the MXV11, the baud rate is finally set to 38.4 Kbps. The longer version follows...

There are three wire-wrap posts that control the baud rate of SLU1, which in my case is the console: J7, J8 and J9. According to the manual I needed to connect J7 to J9. I had a small reel of wire-wrapping wire, but no tool to wrap the posts. As it was only temporary for now, I just manually turned the wire tightly around the posts. A multimeter confirmed the posts were electrically connected, so I plugged in the card, set the terminal speed on my Linux box, and started the PDP. Just as before: no text on the screen.

I was now starting to wonder what could possibly be wrong. As the card was working fine at 9600 bps, I knew the other jumpers were correct. I fell back on the first rule of problem solving: see if it's already been solved. A search of the web turned up another document about the MXV11-B which had conflicting data on the function these particular jumpers. This new document said I needed to connect all three posts to get 38.4K, which I figured I might as well try. Unfortunately, that didn't work either, but all was not lost: I had inadvertedly set the thing to 1200 bps, which agrees with the original manual.

This was the eureka moment for this particular problem: maybe connecting J7 to J9, as I had originally done, did work, but had set the baud rate to something other than 38.4K. And surely enough, replacing that dodgy wire-wrap set the card to 300 bps. So, having had the thing working at every single supported baud rate except the one I actually wanted, the process of elimination had left me with one option: set up the card according to the original manual's configuration for 300 bps. This involves connecting J8 and J9 which, being next to eachother, are easily connected with a regular push-on jumper, eliminating the need for any wire-wrapping. Jumper on, card in and power up - the console was finally running at 38.4 Kbps.

The moral of this story: always RTFM, but don't always trust it!

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