AMD Am186 Series, Instruction Set

Page: 244 / 320

Instruction Set 4-204
RET RET
Examples
This example writes a zero-terminated string to the serial port in polled mode. The full
address (segment:offset) of the string is passed as an input parameter on the stack.
Tips
The assembler automatically generates a different machine-language opcode for RET
depending on the type of procedure (near or far) in which it is used.
Related Instructions
If you want to See
Call a procedure CALL
Reserve storage on the stack for the local variables of a procedure ENTER
Resume an interrupted procedure IRET
Stop executing the current sequence of instructions and begin another sequence JMP
Remove the local variables of a procedure from the stack LEAVE
; initialize and program serial port for transmit
...
; write zero-terminated string to serial port in polled mode
; input parameters: offset of string pushed on stack
segment of string pushed on stack
SendSerialString PROC NEAR
MOV BP,SP ; use BP to access parameters
PUSHA ; save general registers
PUSH DS ; save DS
MOV AX,[BP]+2 ; get segment of string
MOV DS,AX ; DS points to string segment
MOV AX,[BP]+4 ; get offset of string
MOV SI,AX ; SI points to string offset
CLD ; process string from low to high
SENDSS_LOOP:
LODSB ; load byte from string to AL
CMP AL,0 ; is character a null?
JZ SENDSS_DONE ; if so, then done
mSPRT_TXCHAR_P ; transmit character (macro)
JMP SENDSS_LOOP ; jump to top of loop
SENDSS_DONE:
POP DS ; restore saved DS
POPA ; restore general registers
RET 4 ; pop string address and return
SendSerialString ENDP