Diag8 documentation

I am new to this group but have used Hercules for some time. I am
having difficulty finding any documentation for the DIAG8 interface
which I understand can be used to send commands to the Hercules
console. I am interested in this interface in order to trap WTOR tape
mount messages and issue the appropriate devinit command to Hercules
(at least for input tapes).

Any help would be appreciated. Thanks