Just in case you are interested with ASA machine code.
This will give you a feel for the
Registers, Instruction Set, etc..
used by ASA (Assembler for AXE10):-
652. RECEIVE EMDBLO; 016B
652. MFR AR1- PR0; 05F3 016B
652. WSA 16- DR0; (RPEMADDR) 1902 016C
655. MFR AR0- AR1; 7DE3 016D
656. MFR PR0- AR0; 7813 016E
656. RSA DR0- 18; (STATE) 1921 016F
656. JEC DR0, 6, %EMH030%430; 070D1996 0170
658. EP; 00FD 0172
664. RECEIVE EMRECALLACK; 0173
668. RSA DR1- 5; (COWNREF) 1C51 0173
668. MFR PR0- DR0; 1813 0174
668. SSIB DR1, CONTINUEC; 90061E6D 0175
670. EP; 00FD 0177