用PIC低档单片机模拟串口通讯.

2016-06-02 来源：eefocus

串口通讯一般需要单片机带串口通讯接口,而此类单片机一般较贵,可否用普通单片机做串口通讯?

答案是肯定的,但是,通常用于发送数据,接收数据相对就麻烦一些.

串口通讯的原理我就不讲了,各位可以去查询相关的书籍,以下是我做的用于IPOD控制的串口通讯程序.是用普通的PIC12F508单片机实现的.由于我比较穷,没有买IPOD,所以程序是否能正常运作并没有实践过,在此声明.此程序只做抛砖引玉之用.

;IPOD REMOTE CONTROL PORGRAM
;                   vcc +----V-----+ groud
;           PLAY/PAUSE |       GP0|TxD--->IPOD
;                  VOL+ |       GP1|FORWARD>>
;                  VOL- |       GP2|REVERSE<<
;                       +----------+
; 4M InterOTC     1us/Instruction
; 9600bps 104us/bit    so 104 cycles/bit   only for G2 Spec
; Rate is 19200 baud (52 cycles /bit @ 4M) ||| for G3 Spec
; 8N1 DATA TRANS FORMAT 0 <--------> 1    (Startbit:0 + 1byte data+Stop bit:1)
; Author: Deng Chunlin.by 2006-3-23.                   mailto: denjackson@163.com
;*
   list      p=12f508           ; list directive to define processor
   #include        ; processor specific variable definitions
   __CONFIG   _CP_ON & _WDT_OFF & _MCLRE_OFF & _IntRC_OSC

;*
;define varibal and macro
;
GPI0    EQU 6
TIMER0 EQU 1
STATUS EQU 3
OSCCAL EQU 5
w       EQU H'0000'
f       EQU H'0001'
Z       EQU H'0002'
C       EQU H'0000'
Tx      EQU 0
Fw      EQU 1
Rw      EQU 2
Vd      EQU 3
Vp      EQU 4
Pa      EQU 5
Txbyte EQU 7H ;Trans data register.
bitcnt EQU 8H ;Trans bit counts
temp    EQU 9H ; delay temp varibal
temp2   EQU 10H ; delay temp varial2
Txipod1 EQU 11H ; command temp1
Txipod2 EQU 12H ; command temp2

;
   ORG 00H
   NOP
   movwf OSCCAL ;Enter Inter RC OSC Fix tax.
   MOVLW 07H     ;1:256 set to Timer0
   OPTION
   MOVLW B'00111110'     ;GP0 OUT,Other ports In
   TRIS 6
; bcf GPIO,Tx
   goto main
;SUB Program Area*

;*delay sub program*
;* delay sub program.
; Input register:temp
; cycles=3*x+2+2+2=3x+6.
;
UART_delay
     decfsz temp,f            ;1/2 cycle
     goto UART_delay          ;2 cycles
     retlw 0                  ;2 cycles
;ipod putchar*
;* ipod putchar
;* This subroutine transmits the byte stored in the 'TXbyte' register
;*xxxx Rate is 9600 baud (=104 cycles/bit @ 4MHz) !!! from g2 spec!!
;* Rate is 19200 baud (52 cycles /bit @ 4M) ||| for G3 Spec
;* input:     TXbyte
;* registers: bitcnt, TXbyte, temp
;* stack:     one level (UART_delay)
;
iputchar
    movlw D'10'
    movwf bitcnt
iputchar0
    comf Txbyte,f
    setc   ;Set C=1
iputchar1    ;                                                ---         ---
    skpc ; if C=1 then jump else c=0 then jump to iputchar2. 2           1
    goto iputchar2 ;                                                       2
    bcf GPIO,Tx ; Send a '0'                                  1
    goto iputchar3 ;                                           2
iputchar2
    bsf GPIO,Tx ; Send a '1'                                               1
    nop         ;                                                          1
iputchar3
    movlw D'14' ;                                              1           1
    movwf temp ;                                              1           1
;---------------------------------------------------------------------------------
il decfsz temp,f   ;1/2
    goto il          ;2
                     ;                                        42          42
;---------------------------------------------------------------------------------
    rrf Txbyte,f ; >> right move a bit. f(0) to c.            1           1
    decfsz bitcnt,f ; 10 bits all are be sended?               1           1
    goto iputchar1 ;not, go on to send left bits.              2           2
    retlw 0
;*ipod_packet*
;* G3 iPod output routine - ipod_packet
;*
;* Format: output normally low
;*        | output high, 500 uSec
;*        | output message @ 8N1, 9600 baud, lsb first
;*        | output high 4 extra bits
;*    loop| low for ~11.16 mSec
;*
;*   VOL+             0x55 0x03 0x02 0x00 0x02 0xE9
;*   VOL-             0x55 0x03 0x02 0x00 0x04 0xF7
;*   SKIP>>           0x55 0x03 0x02 0x00 0x10 0xEB
;*   < ;*   PLAY/PAUSE       0x55 0x03 0x02 0x00 0x01 0xFA
;*   (button release) 0x55 0x03 0x02 0x00 0x00 0xFB
;*                                     Txipod1 Txipod2
;* input: TXipod1-2 has these bytes --------^^   ^^
;* stack: uses 2 stack locations (iputchar > UARTdelay)
;
ipod_packet
   movlw 0       ;Stop bit.(inverted from 1 to 0)
   movwf Txbyte
   movlw D'10'   ;send 10 stop bits(500us)??
   movwf bitcnt ;1 start bit +8 data bits+1 stop bit=10 bits
   call iputchar2 ;alternate entry doesn't have start bit.
   movlw 055H
   movwf Txbyte
   call iputchar
   movlw 03H
   movwf Txbyte
   call iputchar
   movlw 02H
   movwf Txbyte
   call iputchar
   movlw 0
   movwf Txbyte
   call iputchar

   movf Txipod1,w
   movwf Txbyte
   call iputchar

   movf Txipod2,w
   movwf Txbyte
   movlw D'14' ;1 startbit+8 data bits+1 stopbit+4 extra stop bits.
   movwf bitcnt
   call iputchar0

   bcf GPIO,Tx ;bring back down to 0

   movlw D'14'          ;
   movwf temp2          ;
   movlw 0              ; 0-1,will be overflow to 255.
   movwf temp           ; (774+3)*14~=11ms
lp1            ; delay about 11ms?
   call UART_delay      ; 256*3+6=774 clock.
   decfsz temp2,f       ;
   goto lp1             ;
   retlw 0
;*
delay
     clrf TIMER0
d1s MOVLW D'255' ;
     SUBWF TIMER0,w ;TIMER0
     BTFSS STATUS,Z ;
     GOTO d1s
     retlw 0
;main loop
;
;
;
main
    call delay
    btfss GPIO,Fw
    goto fwd
    nop
    nop
    btfss GPIO,Rw
    goto rev
    nop
    nop
    btfss GPIO,Vd
    goto vdo
    nop
    nop
    btfss GPIO,Vp
    goto vpl
    nop
    nop
    btfss GPIO,Pa
    goto pypa
    nop
    goto main


fwd
    movlw 010H
    movwf Txipod1
    movlw 0EBH
    movwf Txipod2
    call ipod_packet
    btfss GPIO,Fw
    goto fwd
    goto rel ;goto release....
rev
    movlw 08H
    movwf Txipod1
    movlw 0F3H
    movwf Txipod2
    call ipod_packet
    btfss GPIO,Rw
    goto rev
    goto rel ;goto release....
vdo
    movlw 04H
    movwf Txipod1
    movlw 0F7H
    movwf Txipod2
    call ipod_packet
    btfss GPIO,Vd
    goto vdo
    goto rel ;goto release....
vpl
    movlw 02H
    movwf Txipod1
    movlw 0E9H
    movwf Txipod2
    call ipod_packet
    btfss GPIO,Vp
    goto vpl
    goto rel ;goto release....
pypa
    movlw 01H
    movwf Txipod1
    movlw 0FAH
    movwf Txipod2
    call ipod_packet
    btfss GPIO,Pa
    goto pypa
    goto rel ;goto release....
rel
    movlw 0
    movwf Txipod1
    movlw 0FBH
    movwf Txipod2
    call ipod_packet
    goto main

   end

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