It depends on the exact firmware for the unit you have, but the T40 are actually pretty reasonable units. The one I have you can communicate with over r232, and as you already saw in the manual the command to turn it on is just the ascii 'ON'. The one tricky bit is that you need to have xon/xoff handshaking turned on (but not cts/rts) and the right line termination. It has been a while since I used one without a laser head connected, but I think the commands to set the current are the same as for constant current mode for a millenia. You might try looking for a manual for a BL10, it uses the same series power supply and normaly and does not have a head eeprom so the J40/T40 is used in 'just turn on the diodes' mode.