Abstract: This application note provides the hardware connection and software routines for the MAX6900 RTC and 8051-bit controller.
Description This application note describes the connection between the MAX6900 I²C-compatible RTC (real-time clock) and an 8051 microcontroller (µC), and provides program code for the basic interface. The microcontroller used in this example is DS2250, and the software is written in C language. Operation process This program uses two general-purpose ports of the microcontroller as the I²C bus master to control, and the MAX6900 acts as a slave device on the same bus.
The circuit schematic is shown in Figure 1, and the program list is shown in Figure 2.
Enlarged image Figure 1. Schematic of daughter card
Figure 2. Program list / ******************************************** ******************************* / / * 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 ("Enter the Read AddressADDRESS (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 ("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); 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 ("% 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 ("RAM contents"); for (j = 0; j <30; ++ j) {if (! (j% 8)) printf (""); printf ("% 2.bX", I2Cread (ACK ));} printf ("% 2bX", I2Cread (NACK)); / * last byte, NACK * / I2Cstop (); printf ("");} 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 ("MAX6900 build% s", __DATE__); printf ("CI Clock Init"); printf ("CR Clock Read BW Byte Write "); printf (" RR RAM Read RW RAM Write "); printf (" Enter Menu Selection: "); M = _getkey (); switch (M) {case 'B': case 'b': printf ("Byte: B"); M1 = _getkey (); switch (M1) {case 'W': case 'w': w ritebyte6900 (); break;} break; case 'C': case 'c': printf ("Enter 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 ("Enter 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;}}}
Description This application note describes the connection between the MAX6900 I²C-compatible RTC (real-time clock) and an 8051 microcontroller (µC), and provides program code for the basic interface. The microcontroller used in this example is DS2250, and the software is written in C language. Operation process This program uses two general-purpose ports of the microcontroller as the I²C bus master to control, and the MAX6900 acts as a slave device on the same bus.
The circuit schematic is shown in Figure 1, and the program list is shown in Figure 2.
Enlarged image Figure 1. Schematic of daughter card
Figure 2. Program list / ******************************************** ******************************* / / * DEMO6900.c * / / ********** ************************************************** *************** / / * This program is for example only and is not supported by Dallas Maxim * / #include
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