摘要：本应用笔记提供了MAX6900 RTC与8051位控制器的硬件连接和软件例程。

说明

本应用笔迹介绍了MAX6900 I²C兼容RTC (实时时钟)与8051微控制器(µC)之间的连接方式，并提供了用于基本接口的程序代码。本范例中所使用的微控制器是DS2250, 软件用C语言编写。

操作过程

本程序利用作为I²C总线主机的微控制器的两个通用端口进行控制，MAX6900则作为同一总线上的从机器件。

电路原理图如图1所示，程序清单如图2所示。


放大图形
图1. 子卡原理图

图2. 程序清单

/***************************************************************************/ /* DEMO6900。c */ /***************************************************************************/ /* This program is for example only and is not supported by Dallas Maxim */ #include  /* Prototypes for I/O funcTIons */ #include  /* Register declaraTIons for DS5000 */ #define ACK 0 #define NACK 1 #define ADD6900 0xa0 /* 2-wire addresses */ sbit scl = P0^0; /* 2-wire pin definiTIons */ sbit sda = P0^1; void I2Cstart(); void I2Cstop(); uchar I2Cwrite(uchar); unsigned char I2Cread(int); void writebyte6900(); void IniTIalize_MAX6900(); void disp_clk_regs(); void burstramread(); void burstramwrt(); /* global variables */ void I2Cstart() /* ----------------------------------------------- */ { sda = 1; /* Initiate start condition */ scl = 1; sda = 0; } void I2Cstop() /* ----------------------------------------------- */ { sda = 0; sda = 0; /* Initiate stop condition */ scl = 1; scl = 1; sda = 1; } uchar I2Cwrite(uchar d) /* ----------------------------- */ { int i; scl = 0; for (i = 0;i < 8; i++) { if (d & 0x80) sda = 1; /* Send the msbits first */ else sda = 0; scl = 0; scl = 1; d = d < 1; /* add to scl high time */ scl = 0; } sda = 1; /* Release the sda line */ scl = 0; scl = 1; i = sda; scl = 0; if (i) { puts("Ack missing"); } return(i); } uchar I2Cread(int b) /* ----------------------------------- */ { uchar i, d; d = 0; sda = 1; /* Let go of sda line */ for (i=1; i<=8; i++) /* read the msb first */ { scl = 0; scl = 1; d = d << 1; d = d | (unsigned char)sda; } scl = 0; sda = b; /* Hold sda low for ACK, high for NACK */ scl = 0; /* toggle clock */ scl = 1; scl = 0; sda = 1; /* Release the sda line */ return d; } void writebyte6900() /* ----- write a single byte; user enters read address ----- */ { uchar add; uchar dat; /* Get Address & Data */ printf("\nEnter the Read Address\nADDRESS (80,82,84...FC): "); scanf("%bx", &add); printf("DATA (0-ff):"); scanf("%bx", &dat); I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(add); I2Cwrite(dat); I2Cstop(); } void Initialize_MAX6900() /* ------- initialize from stdio entries ------- */ /* Note: NO error checking is done on the user entries! */ { uchar yr, mn, dt, dy, hr, min, sec, day; I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(0x8e); /* control register write address */ I2Cwrite(0x00); /* clear write protect */ I2Cstop(); printf("\nEnter the year (0-99): "); scanf("%bx", &yr); printf("Enter the month (1-12): "); scanf("%bx", &mn); printf("Enter the date (1-31): "); scanf("%bx", &dt); printf("Enter the day (1-7): "); scanf("%bx", &dy); printf("Enter the hour (1-23): "); scanf("%bx", &hr); hr = hr & 0x3f; /* force clock to 24 hour mode */ printf("Enter the minute (0-59): "); scanf("%bx", &min); printf("Enter the second (0-59): "); scanf("%bx", &sec); I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(0xbe); /* clock burst write */ I2Cwrite(sec); I2Cwrite(min); I2Cwrite(hr); I2Cwrite(dt); I2Cwrite(mn); I2Cwrite(dy); I2Cwrite(yr); I2Cwrite(0); /* control */ I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(0x92); I2Cwrite(0x20); /* century data */ I2Cstop(); } void disp_clk_regs() /* --------- display using burst mode --------- */ { uchar Sec, prv_sec = 99, Min, Hrs, Dte, Mon, Day, Yr, cy; while(!RI) /* Read & Display Clock Registers */ { I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(0xbf); /* clock burst read */ I2Cstart(); I2Cwrite(ADD6900 + 1); /* slave address + read */ Sec = I2Cread(ACK); /* starts w/last address stored in register pointer */ Min = I2Cread(ACK); Hrs = I2Cread(ACK); Dte = I2Cread(ACK); Mon = I2Cread(ACK); Day = I2Cread(ACK); Yr = I2Cread(ACK); cy = I2Cread(NACK); /* dummy read of control register */ I2Cstart(); I2Cwrite(ADD6900); /* slave address + write */ I2Cwrite(0x93); /* century byte read address */ I2Cstart(); I2Cwrite(ADD6900 + 1); /* slave address + read */ cy = I2Cread(NACK); I2Cstop(); if(Sec != prv_sec) /* display every time seconds change */ { printf("\n%02bX%02bX/%02bX/%02bX %01bX", cy, Yr, Mon, Dte, Day); printf(" %02bX:%02bX:%02bX", Hrs, Min, Sec); } prv_sec = Sec; } RI = 0; /* Swallow keypress to exit loop */ } void burstramread() /* ----------------------------------------- */ { uchar j, k; I2Cstart(); I2Cwrite(ADD6900); /* write slave address, write 6900 */ I2Cwrite(0xff); /* ram burst read */ I2Cstart(); I2Cwrite(ADD6900 + 1); /* slave address + read */ printf("\nRAM contents"); for (j=0; j<30; ++j) { if(!(j % 8) ) printf("\n"); printf("%2.bX ", I2Cread(ACK) ); } printf("%2bX", I2Cread(NACK) ); /* last byte, NACK */ I2Cstop(); printf("\n"); } void burstramwrt(uchar Data) /* ----------------------------------------- */ { uchar j, k; I2Cstart(); I2Cwrite(ADD6900); /* write slave address, write 6900 */ I2Cwrite(0xfe); /* ram burst write */ for (k=0; k < 31; ++k) { I2Cwrite(Data); } I2Cstop(); } main (void) /* ----------------------------------------------------- */ { uchar i, M, M1; while (1) { printf("\nMAX6900 build %s\n", __DATE__); printf("CI Clock Init\n"); printf("CR Clock Read BW Byte Write\n"); printf("RR RAM Read RW RAM Write\n"); printf("Enter Menu Selection: "); M = _getkey(); switch(M) { case 'B': case 'b': printf("\rByte: B"); M1 = _getkey(); switch(M1) { case 'W': case 'w': writebyte6900(); break; } break; case 'C': case 'c': printf("\rEnter Clock Routine to run:C"); M1 = _getkey(); switch(M1) { case 'I': case 'i': Initialize_MAX6900(); break; case 'R': case 'r': disp_clk_regs(); break; } break; case 'R': case 'r': printf("\rEnter Ram Routine to run:R"); M1 = _getkey(); switch(M1) { case 'R': case 'r': burstramread(); break; case 'W': case 'w': printf("\nEnter the data to write: "); scanf("%bx", &i); burstramwrt(i); break; } break; } } }