If the terminal is old, there’s a good chance the lithium backup battery has failed and the NVR (non volatile RAM) will have lost it’s settings that dictates the communication interface speed – without this parameter the VDU cannot load it’s workstation program from the host computer, so the DAP4 will just sit there and not do anything.
This short video sequence shows how to enter the default setting – 0815. This specifies a communication speed of 9600 baud.
You MUST enter this sequence as soon as you turn the VDU on from the keyboard. If you make a mistake you have to switch off, and back on again. Also, you have to use the numeric keypad and the CR key as shown. Don’t try this user the numbers above the main keyboard area, or the large CR key as it won’t work and you will have to start again.
I seem to remember that parameters 0812 were used for 1200 baud (we used to connect DAP4s directly to modems for customer remote support purposes).
This would mean that:
- 0816 – 19.2K baud
- 0815 – 9600 baud
- 0814 – 4800 baud
- 0813 – 2400 baud
- 0812 – 1200 baud
I’m only certain of 0815… the rest is pure theory. In the UK at least, all terminals were set to 9600 baud.
However, check the ALME settings for the channel in question. It may be sensible to start at 9600 baud at both ends as this was the most common speed setting (at least in the UK), and then experiment from there.
If the workstation starts to load you will see L1 and L2 flashing alternatively and then after a few seconds L4 will illuminate. At this point you should hear the HT voltage that powers the VDU tube engage; a slight static electricity type sound. You should see “CR” appear on the display within 30 seconds. If not, check the brightness and contrast controls – located in the PSU near the mains power switch – back top right corner.