I/O Exit Access to Control Blocks

On entry to the exit, register 1 (R1) contains the address of the pointer to the EXTCB (Exit Control Block). The parameter list addresses point to a 2-byte length followed by the value.

All parameter lists end with the high order bit on in the last address in the list. The macro DGA$XTCB generates the EXTCB. DGA$XTCB is supplied in the $CD.SDGAMAC library.