要：该应用笔记演示了MAX6901与8051微控制器的连接方式，并提供了基本的接口程序例程。本文采用的微控制器是DS2250，软件用C语言编写。

MAX6901引脚配置

概述

该应用笔记演示了MAX6901与8051微控制器的连接方式，并提供了基本的接口程序例程。本文采用的微控制器是DS2250，软件用C语言编写。

工作原理

该程序利用微控制器的三个通用端口引脚控制3线总线。微控制器向MAX6901发送一个命令/地址字节，启动数据传输。随后，微控制器向MAX6901发送其它字节或提供SCLK，根据命令字节发送或接收数据。

电路原理图如图1所示，软件如图2所示。


图1. 子卡原理图"(PDF下载)

图2. 代码列表

/***************************************************************************/ /* DEMO6901。c */ /***************************************************************************/ /* #pragma code symbols debug */ #include
         
          /* Prototypes for I/O funcTIons */ #include
          
           /* Register declaraTIons for DS5000 */ /***************************** Defines ********************************/ sbit CE = P0^0; sbit SCLK = P0^1; sbit IO = P0^2; /*********************** FuncTIon Prototypes **************************/ void writebyte(); void iniTIalize(); void disp_clk_regs(); void burstramread(); void burstramwrt(); /************************* Global Variables ***************************/ uchar cy, yr, mn, dt, dy, hr, min, sec, msec; void reset_3w() /* ---- reset the 3-wire interface ---- */ { SCLK = 0; CE = 0; IO = 0; /* program IO pin to 0V */ } void wbyte_3w(uchar W_Byte) /* --- write one byte to the DUT --- */ { uchar i; CE = 1; for(i = 0; i < 8; ++i) { if(W_Byte & 0x01) IO = 1; /* set port pin high to read data */ else IO = 0; SCLK = 0; SCLK = 1; W_Byte >>= 1; } } uchar rbyte_3w() /* --- read one byte from the DUT --- */ { uchar i; uchar R_Byte = 0; CE = 1; IO = 1; for(i=0; i<8; ++i) { SCLK = 1; SCLK = 0; if(IO) { R_Byte >>= 1; R_Byte += 0x80; } else R_Byte >>= 1; } return R_Byte; } void writebyte() /* ----- write one byte, prompt for address and data ------ */ { uchar add; uchar dat; /* Get Address & Data */ printf(" Enter the Write Address (h) ADDRESS (80,82,84...):"); scanf("%bx", &add); printf("DATA (0-ff):"); scanf("%bx", &dat); reset_3w(); wbyte_3w(add); wbyte_3w(dat); reset_3w(); } void initialize() /* ----- init clock data using user entries ----- */ /* Note: NO error checking is done on the user entries! */ { reset_3w(); wbyte_3w(0x0f); /* control register write address */ wbyte_3w(0x00); /* clear write protect */ reset_3w(); printf(" Enter 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); reset_3w(); wbyte_3w(0xbe); /* clock burst write */ wbyte_3w(sec); wbyte_3w(min); wbyte_3w(hr); wbyte_3w(dt); wbyte_3w(mn); wbyte_3w(dy); wbyte_3w(yr); wbyte_3w(0); /* control */ reset_3w(); wbyte_3w(0x92); wbyte_3w(0x20); /* century data */ reset_3w(); } void disp_clk_regs() /* --- loop reading clock, display when secs change --- */ { uchar mil, pm, prv_sec = 99; while(!RI) /* Read & Display Clock Registers */ { reset_3w(); wbyte_3w(0xbf); /* clock burst read */ sec = rbyte_3w(); min = rbyte_3w(); hr = rbyte_3w(); dt = rbyte_3w(); mn = rbyte_3w(); dy = rbyte_3w(); yr = rbyte_3w(); cy = rbyte_3w(); /* dummy read of control register */ reset_3w(); wbyte_3w(0x93); /* century byte read address */ cy = rbyte_3w(); reset_3w(); if(hr & 0x80) mil = 0; else mil = 1; if(sec != prv_sec) /* display every time seconds change */ { if(mil) { printf(" %02bX%02bX/%02bX/%02bX %01bX", cy, yr, mn, dt, dy); printf(" %02bX:%02bX:%02bX", hr, min, sec); } else { if(hr & 0x20) pm = 'P'; else pm = 'A'; hr &= 0x1f; /* strip mode and am/pm bits */ printf(" %02bx%02bx/%02bx/%02bx %02bx", cy, yr, (mn & 0x1f), dt, dy); printf(" %02bx:%02bx:%02bx %cM", hr, min, sec, pm); } } prv_sec = sec; } RI = 0; /* Swallow keypress to exit loop */ } void burstramread() /* ------ read RAM using burst mode ----- */ { uchar k; printf(" MAX6901 RAM contents: "); reset_3w(); wbyte_3w(0xff); /* ram burst read */ for (k = 0; k < 31; k++) { if(!(k % 8) ) printf(" "); printf("%02.bX ", rbyte_3w() ); } reset_3w(); } void burstramwrt(uchar Data) /* ------ write RAM using burst mode ------- */ { uchar j, k; reset_3w(); wbyte_3w(0xfe); /* ram burst write */ for (k=0; k < 31; ++k) { wbyte_3w(Data); } reset_3w(); } main (void) /* ----------------------------------------------------- */ { uchar i, M, M1; while (1) { printf(" MAX6901 build %s ", __DATE__); printf("CI Clock Init "); printf("CR Clock Read CW Clock Write "); printf("RR Read RAM RW RAM Write "); printf("Enter Menu Selection: "); M = _getkey(); switch(M) { case 'C': case 'c': printf("\rEnter Clock Routine to run:C"); M1 = _getkey(); switch(M1) { case 'I': case 'i': initialize(); break; case 'R': case 'r': disp_clk_regs(); break; case 'W': case 'w': writebyte(); 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(" Enter the data to write: "); scanf("%bx", &i); burstramwrt(i); break; } break; } } }