DS1305 è un Real Time Clock con porta I2C. Ecco come utilizzarlo con un PIC16F628 e come monitorarlo attraverso una connessione seriale RS232.
REAL TIME CLOCK SPI CON PIC16F628
Lo schema di figura 1 mostra la connessione tra il modulo RTC ed il PIC, connessione effettuata mediante interfaccia SPI a tre fili. Per questa applicazione è possibile utilizzare anche un DS1306. Il PIC legge i dati dal DS1305 e li invia ad un PC attraverso una connessione RS232. La linea DTR della porta seriale è utilizzata per resettare il PIC ed avviare quindi il programma. La conversione dei livelli TTL/RS232 viene effettuata con un DS232. Il listato 1 riporta il sorgente assembler/assembly da utilizzare nel PIC.
Figura 1. Schema elettrico per la connessione del RTC al PIC
#include <P16F628.inc> list p=16F628 __config H’3F2A’ #define BAUD_VALUE 0x15 #define SPI_CLK PORTA,1 #define SPI_MOSI PORTA,2 #define SPI_MISO PORTA,3 #define SPI_CE PORTA,4 SCRATCH equ 0x40 TMP equ 0x41 TMP2 equ 0x42 COUNT equ 0x43 YRS equ 0x44 MON equ 0x45 DOW equ 0x46 DAYS equ 0x47 HRS equ 0x48 MINS equ 0x49 SECS equ 0x4a user_bits equ 0x2C save_w equ 0x38 save_status equ 0x39 SET_BANK0 MACRO bcf STATUS, RP0 bcf STATUS, RP1 ENDM SET_BANK1 MACRO bsf STATUS, RP0 bcf STATUS, RP1 ENDM org 0x00 RESET: goto START ;——————————-———-—————————— ;—-— start ———————-——————— ;——————————-———-———-—————— org 0x0A START: SET_BANK0 movlw 0x07 movwf CMCON SET_BANK1 movlw 0x00 movwf VRCON SET_BANK0 clrf PORTA movlw 0x08 SET_BANK1 movwf TRISA bsf OPTION_REG, 7 SET_BANK0 movlw 0x07 movwf CMCON call uart_init CheckForCommands: movlw banner-1 call write call uart_getchar call uart_putchar movwf TMP bcf TMP,5 movf TMP,W xorlw ‘S’ btfss STATUS,Z goto not_ss call set_clock goto CheckForCommands not_ss: movf TMP,W xorlw ‘R’ btfss STATUS,Z goto not_rr call read_clock goto CheckForCommands not_rr: goto CheckForCommands ;———————-———————-————————— ;—- uart routines ;——————————————-—————————— uart_putchar: charwait1: btfss PIR1, TXIF goto charwait1 movwf TXREG return ;————————————————————————— uart_getchar: charwait2: btfss PIR1, RCIF goto charwait2 movfw RCREG return ;——-—————————————————————— uart_init: SET_BANK1 movlw BAUD_VALUE movwf SPBRG bcf TXSTA, SYNC bsf TXSTA, BRGH bsf TXSTA, TXEN bcf PIE1, RCIE SET_BANK0 bsf RCSTA, SPEN bsf RCSTA, CREN return ; return ;———————————————————————— banner: dt “\n\rDS1305 SPI DEMO\n“ dt “\rR)ead time S)et” dt “time\n\r”,0h year: dt “\n\rYear (0-99): “,0h month: dt “Month (1-12): “,0h dow: dt“Day of Week (1-7): “,0h date: dt“Date(1-28,29,30,31):“,0h hour: dt “Hour (0-23): “,0h minute: dt “Minute (0-59): “,0h second: dt “Second (0-59): “,0h ;—character conversion — ;— ascii to bcd ———- readbcd: clrf TMP gobcd: call uart_getchar call uart_putchar xorlw 0dh btfss STATUS,Z goto bcd movf TMP,W return bcd: xorlw 0dh addlw -30h btfsc W,4 addlw -7 digit: andlw 0x0f bcf TMP,4 bcf TMP,5 bcf TMP,6 bcf TMP,7 movwf SCRATCH movf TMP,W movwf TMP2 movf SCRATCH,W movwf TMP movf TMP2,W swapf TMP2,W iorwf TMP,W movwf TMP goto gobcd ;— convert bcd to ascii — ;— entry: W=bcd value ;— exit: W=last ascii writebcd: movwf TMP swapf TMP,W andlw 0x0f addlw 0x06 btfss STATUS,DC goto lessnine addlw 0x31 goto digit1 lessnine: addlw 0x2a digit1: call uart_putchar movf TMP,W andlw 0x0f addlw 0x06 btfss STATUS,DC goto lessnine2 addlw 0x31 goto digit2 lessnine2: addlw 0x2a digit2: call uart_putchar return ;— display RTC data — read_clock: call RTC_brst_rd read_regs: movf YRS,W call writebcd movlw ‘/‘ call uart_putchar movf MON,W call writebcd movlw ‘/‘ call uart_putchar movf DAYS,W call writebcd movlw ‘ ‘ call uart_putchar movf DOW,W call writebcd movlw ‘ ‘ call uart_putchar movf HRS,W call writebcd movlw ‘:’ call uart_putchar movf MINS,W call writebcd movlw ‘:’ call uart_putchar movf SECS,W call writebcd movlw 0x0d call uart_putchar return ;— write to the RTC ———- set_clock: movlw year-1 call write call readbcd movwf YRS movlw month-1 call write call readbcd movwf MON movlw date-1 call write call readbcd movwf DAYS movlw dow-1 call write call readbcd movwf DOW movlw hour-1 call write call readbcd movwf HRS movlw minute-1 call write call readbcd movwf MINS movlw second-1 call write call readbcd movwf SECS call RTC_brst_wr return ;— RTC routines ————-———- RTC_brst_rd: bsf SPI_CLK bsf SPI_CE movlw 0h call write_RTC call read_RTC movwf SECS call read_RTC movwf MINS call read_RTC movwf HRS call read_RTC movwf DOW call read_RTC movwf DAYS call read_RTC movwf MON call read_RTC movwf YRS bcf SPI_CE return RTC_brst_wr: bsf SPI_CLK bsf SPI_CE movlw 08fh call write_RTC movlw 0 call write_RTC bcf SPI_CE bsf SPI_CLK bsf SPI_CE movlw 08fh call write_RTC movlw 0 call write_RTC bcf SPI_CE bsf SPI_CLK bsf SPI_CE movlw 80h call write_RTC movf SECS, W call write_RTC movf MINS, W call write_RTC movf HRS, W call write_RTC movf DOW, W call write_RTC movf DAYS, W call write_RTC movf MON, W call write_RTC movf YRS, W call write_RTC bcf SPI_CE return ;—— Read RTC into W ———- read_RTC: movlw 08h ;Send 8 bits movwf COUNT SPI_read_loop: rlf TMP, 1 bcf SPI_CLK bcf TMP, 0 btfsc SPI_MISO bsf TMP, 0 bsf SPI_CLK decfsz COUNT, 1 goto SPI_read_loop movf TMP, W return ;—- Write the W to RTC —- write_RTC: movwf TMP SPI_write: movlw 08h movwf COUNT SPI_w_loop: bcf SPI_CLK bcf SPI_MOSI btfsc TMP, 7 bsf SPI_MOSI SPI_w_cont: rlf TMP, 1 bsf SPI_CLK decfsz COUNT, 1 goto SPI_w_loop return pclsub: incf SCRATCH,F movf SCRATCH,W movwf PCL ;— write a string to ; USART ————-———-———-———- write: movwf SCRATCH GoWrite: call pclsub addlw 0h btfsc STATUS,Z return call uart_putchar goto GoWrite END
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Un interessante layout per implementare un clock real time sul PIC16F. Il chip della Maxim Integrated fornisce un binary coded decimal (BCD) e la possibilità di essere alimentato con una batteria ricaricabile in veste di “backup” per l’alimentazione.