QBUS CPU ODT
From Computer History Wiki
ODT (Octal Debugging Technique) on QBUS PDP-11s is effectively their front panel. These CPUs do not have a front panel to control them; instead, as a cost-reduction measure, when the CPU is halted, specialized microcode uses the main serial line as a operating console. There are commands to read and write main memory, start the CPU, etc.
The command set is:
- '/' - open location
- '<CR>' - close open location
- '<LF>' - open next location
- 'G' - start CPU
- 'P' - proceed CPU after halt
The main serial interface is normally configured so that when the CPU is running, sending a break on the console serial line halts the CPU. (Depending on which interface card is used, some can be set to bootstrap the machine instead.)
