RCA COSMAC User Manual page 56

COSMAC Microprocessor
55
START
~'"
M ADDRESS M BYTE OPERATION COMMENTS
0100 03
3+P
1
GO TO SUBROUTINE
0101 96 RI61.1+D SAVE LAST RETURN
0102 52 D+MIR1211
POINTER ON DC STACK
0103 22 DECR RI21
0104 86 R 161.O+D
0105 52 D+MIRI211
0106
22 DECR RI21
0107 93 RI31.1+D
}
SAVE NEW RETURN
0108 B6 D'RI61.1 POINTER IN RI61
0109
83
RI31.O+D
010A A6 D+RI61.0
010B 46
MIR(61)+D; R(6) +J
LOAD SUBROUTINE ADDRESS
010C
B3 D+R(3).1 USING RETURN POINTER
010D
46 MIR(6))+D; R(6) +1
010E
A3 D·R(3).0
}
010F 30 BR
GO TO TOP
0110 00
Fig. 60 - Subroutine call sequence with rep/oaded entry at 0101.
START
~'"'
M ADDRESS M BYTE OPERATION COMMENTS
0200 D3 3+P RETURN TO ORIGINAL PROGRAM
0201
86
R(6).O+D
}
FETCH ADDRESS OF NEXT
0202 A3 D+R(3).0 INSTRUCTION OF
0203 96 R(6) l+D ORIGINAL PROGRAM
0204 B3 D~·R (3). 1
0205 E2
2+X }
0206 12 INCREMENT R(2)
SET UP STACK POINTER
0207 42
M' "'"
'0 " "
"j
RESTORE LAST
0208 A6 D+R(6).0 RETURN POINTER
0209 FO MIR(2))+D
020A 86
D+R(6).1
020B 30 BR
}
GO TO TOP
020C 00
Note that after a subroutine return using this mechanism, X equal, 2.
Fig. 61 - Subroutine return sequence with pre/oaded entry at 0201.