1. Subroutine Call; Stack

2. stack Structure of stack Address Data 0005H 0006H SP  0007H 0008H
000BH
000CH
000DH
000EH
000FH
stack

3. start:
MOV R0,#00H
MOV R1,#11H
MOV R2,#22H
MOV R3,#33H
MOV R4,#44H
MOV R5,#55H
MOV R6,#66H
MOV R7,#77H
NOP
PUSH AR0
PUSH AR1
PUSH AR2
PUSH AR3
PUSH AR4
PUSH AR5
PUSH AR6
PUSH AR7
Before PUSH AR Before PUSH AR Before PUSH AR2
Address
Data
0005H
0006H
0007H
SP 
0008H
00H
0009H ??
000AH
000BH
000CH
000DH
000EH
000FH
Address
Data
0005H
0006H
SP 
0007H
0008H ??
0009H
000AH
000BH
000CH
000DH
000EH
000FH
Address
Data
0005H
0006H
0007H
0008H
00H
SP 
0009H
11H
000AH ??
000BH
000CH
000DH
000EH
000FH

4. NOP
POP 57H
POP 56H
POP 55H
POP 54H
POP 53H
POP 52H
POP 51H
POP 50H
JMP start
Before POP 57H Before POP 56H Before POP 55H
Address
Data
0005H
0006H
0007H
0008H 00
0009H 11
000AH 22
000BH 33
000CH 44
000DH 55
000EH 66
SP 
000FH 77
Address
Data
0005H
0006H
0007H
0008H 00
0009H 11
000AH 22
000BH 33
000CH 44
000DH 55
SP 
000EH 66
000FH 77
Address
Data
0005H
0006H
0007H
0008H 00
0009H 11
000AH 22
000BH 33
000CH 44
SP 
000DH 55
000EH 66
000FH 77

5. ACALL
LCALL
Length of machine code
2 bytes
3 byte

6. Machine code format Target (Subroutine) address = A10A9A8･･･A1A0
Range: 2 K
Target address = A15A14A13･･･A1A0
Range: 64 K

7. Note the convention of EdSim51:
CALL is replaced by ACALL .
JMP is replaced by either SJMP or AJMP.
LCALL and LJMP must be programmed explicitly.

8. Before the LCALL sub instruction has been executed
After the LCALL sub instruction has been executed

9. After the RET instruction has been executed

10. RET

11. ICPs ICP = push & pop - simple.asm ICP = average of 5 numbers.asm
ICP = average of up to 255 numbers.asm
ICP = average of up to 255 numbers - with PSW & registers intact.asm