Pic Compilation Getting Started sample

Tag: value addressing CFS top instruction specifying unit main SWA

Sequential program Structure

20H Unit Low 4-bit out of 21H, high four-bit out of the deposit to 22H
Highlights: ANDLW and SWAPF

  MOVF     20H,0      ;将20H单元的内容送人W  ANDLW    0FH        ;W高四位清零低4位保持不变  MOVWF    21H        ;将拆分后的低4位送21H  SWAPF    20H,0      ;将20H单元内容高、低半字节换位后送W  ANDLW    0FH        ;再将W高四位清0低四位保持不变  MOVWF    22H        ;将拆分后的高四位送22H单元

Branch Program Structure

20H and 21H units in RAM hold 2 numbers to find large deposits in 22H units
Important: Two number subtraction, judging the value of the flag bit C

STATUS    EQU      03H      ;定义STATUS寄存器地址为03HC         EQU      0        ;定义进位/借位标志C在STATUS中得地址为0          MOVF     20H 0    ;将20H单元的内容送人W          SUBWF    21H 0    ;用21H单元的内容减去W中的内容，结果存在W中          BTFSS    STATUS,C ;若C=1，没借位，则21H单元中的数大，跳到F21BIG          GOTO     F20BIG   ;若C=0，有借位，20H单元中得数较大，则跳至F20BIG    F21BIG    MOVF    21H,0     ;将21H中的内容存入W寄存器          MOVWF   22H       ;再将它转存到22H单元          GOTO    STOP      ;跳过下面两条指令到程序末尾        F20BIG    MOVF    20H,0     ;将20H中的内容存入W寄存器          MOVWF   22H       ;再将它转存到22H单元STOP      GOTO    STOP      ;任务完成，停机，原地踏步

Cyclic program Structure

In data memory, 50 cells starting at address 30H are all written to 00H
Important: The indirection register FSR as the address pointer

COUNT   EQU      20H        ;指定20H单元作为循坏次数计数器（即循环变量）FSR     EQU      04H        ;定义FSR寄存器地址为04HINDF    EQU      00H        ;设定INDF寄存器地址为00H        MOVLW    D50        ;把计数器初值50送入W        MOVWF    COUNT      ;再把50转入计数器（作为循环变量的操作值）        MOVLW    30H        ;把30H（起始地址）送入W        MOVWF    FSR        ;再把30H转入寄存器FSR(用作地址指针)        NEXT    CLRF     INDF       ;把以FSR内容为地址所指定的单元清0        INCF     FSR,1      ;地址指针内容加1，指向下一单元        DECFSZ   COUNT,1    ;计数值减1，结果为0就跳过到下一条指令到STOP处        GOTO     NEXT       ;跳转回去并执行下一次循环STOP    GOTO     STOP       ;循环结束之后执行该语句，实现停机

Sub-Program Structure

3-digit Max put into 40H unit

STATUS    EQU        03HC         EQU        00HX         EQU        20HY         EQU        21HZ         EQU        22H

Main program

MAIN    MOVF    30H,0        MOVWF   X        MOVF    21H,0        MOVWF   Y        CALL    SUB        MOVF    Z,0        MOVWF   X        MOVF    32H,0        MOVWF   Y        CALL    SUB        MOVF    Z,0        MOVWF   40HSTOP    GOTO    STOP

Sub-Program

Subroutines: (Entry parameters: X and y, exit parameters: Z)

SUB     MOVF     X,0        ;将X内容送人W        SUBWF    Y,0        ;Y内容减去W内容，结果存入W        BTFSS    STATUS,C   ;若C=1，没有发生借位，执行下一条，否则跳转        GOTO     X_BIG                Y_BIG   MOVF    Y,0         ;将Y中的数据送入W        MOVWF    Z          ;再将它转存到Z        GOTO     THEEND     ;跳过下面两条到末尾        X_BIG   MOVF    X,0         ;将X中的数据送入W        MOVWF    Z          ;再将它转存到ZTHEEND  RETURN              ;子程序返回

Pic Compilation Getting Started sample