Samsung S3C9228/P9228, 8-Bit CMOS Microcontroller user manual Call Call Procedure

SAM88RI INSTRUCTION SET S3C9228/P9228

CALL — Call Procedure

CALL	dst
Operation:	SP	¨	SP – 1
	@SP	¨	PCL
	SP	¨	SP –1
	@SP	¨	PCH
	PC	¨	dst

The current contents of the program counter are pushed onto the top of the stack. The program counter value used is the address of the first instruction following the CALL instruction. The specified destination address is then loaded into the program counter and points to the first instruction of a procedure. At the end of the procedure the return instruction (RET) can be used to return to the original program flow. RET pops the top of the stack back into the program counter.

Flags: No flags are affected.

Format:

opc dst

Bytes	Cycles	Opcode	Addr Mode
		(Hex)	dst
3	14	F6	DA

opc

dst

2 12 F4 IRR

Examples: Given: R0 = 15H, R1 = 21H, PC = 1A47H, and SP = 0B2H:

CALL	1521H	→	SP = 0B0H
			(Memory locations 00H = 1AH, 01H = 4AH, where 4AH
			is the address that follows the instruction.)
CALL	@RR0	→	SP = 0B0H (00H = 1AH, 01H = 49H)

In the first example, if the program counter value is 1A47H and the stack pointer contains the value 0B2H, the statement "CALL 1521H" pushes the current PC value onto the top of the stack. The stack pointer now points to memory location 00H. The PC is then loaded with the value 1521H, the address of the first instruction in the program sequence to be executed.

If the contents of the program counter and stack pointer are the same as in the first example, the statement "CALL @RR0" produces the same result except that the 49H is stored in stack location 01H (because the two-byte instruction format was used). The PC is then loaded with the value 1521H, the address of the first instruction in the program sequence to be executed.

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