8051 汇编语言 - 堆栈指针初始化

Question

考虑到 8051 微型 controller RAM 组织，我想将堆栈指针设置为地址 30h。

我想知道我是否必须在我的程序开始时只做一次，或者是否有必要在 if 语句的 2 个分支中的每个子例程调用之前设置它？ 子程序结束后堆栈是否重置为 7fh？ 还是会在整个程序执行期间保持设置为 30h？ 我的代码如下：

$ NOMOD51
$ INCLUDE (reg517.inc)

ORG 0H  
    MOV R1, #90H    ;load register 1 with address 90h
    MOV @R1, #00H   ;initialize adress 90h indirectly, via register 1
    MOV A, #00H
    ;MOV SP, 30H    ; should this instruction go here???

FORLOOP:
    INC A                       ;increment register 1 by 1
    MOV @R1,A                   ;load the accumulator with the content of 90h indirectly addressed via R1
    CJNE @R1, #3d, IFSTATEMENT  ;if aacumulator contents not 11, jump to condition
    JMP ENDLABEL                ;else jump to end label
    
IFSTATEMENT:
    JNB 23h, SETBIT     ;condtion: if bit 23h is not set, jump to set bit instruction
    JMP CLEARBIT        ;else jump to clear bit instruction
    
SETBIT:
    SETB 23H            ;set memory bit 23h
    MOV P0, #0FFH       ;load all bits of port 0
    MOV SP, 30H         ;set stack pointer to scratch pad area, since we are about to call a subroutine
    ;MOV SP, 30H        ; or here???
    LCALL DELAY         ;call the Delay subroutine
    JMP FORLOOP         ;after 3s jump back to the for loop

CLEARBIT:
    CLR 23h             ;set memory bit 23h
    MOV P0, #00H        ;clear all bits of port 0
    ;MOV SP, 30H        ; or here???
    LCALL DELAY         ;call the Delay subroutine
    JMP FORLOOP         ;after 3s jump back to the for loop

DELAY:                  ;delay of 250 x 250 x 24 instruction cycles = 3000000ums = 3s
    MOV R3, #1d
    L3:
        MOV R2, #1d
    L2:
        MOV R1, #1d
    L1:         
        DJNZ R1, L1
        DJNZ R2, L2
        DJNZ R3, L3
    RET

ENDLABEL:
END

Answer 1

请查阅任何关于 8051 的好书，您会发现：

• SFR SP只需在初始化部分设置一次，并且仅在您对其初始值不满意时才需要设置。
• xCALL和RET会自动增加和减少SP ，并且仅在必要时进行。 你最好别惹它。
• 改变SP的其他常见指令是PUSH和POP 。 您需要使它们保持平衡，直到您确切知道自己在做什么。