DS3234 DSP56F800DEMO RS-232 56F800 RS232 AN4005 APP4005 - Datasheet Archive

 

Keywords: DS3234, SPI Feb 29, 2008 APPLICATION NOTE 4005 Interfacing a DS3234 Extremely Accurate SPI-Bus Real-Time Clock (RTC) to

 

Maxim > App Notes > REAL-TIME CLOCKS Keywords: DS3234 DS3234, SPI Feb 29, 2008 APPLICATION NOTE 4005 Interfacing a DS3234 DS3234 Extremely Accurate SPI-Bus Real-Time Clock (RTC) to a Motorola Digital Signal Processor (DSP) Abstract: This application note provides an example of hardware and software for interfacing an SPITM realtime clock (RTC) to a Motorola® digital signal processor (DSP) that has a built-in SPI-interface module. This example uses a Motorola DSP Demo Kit as the basis for the circuit. Circuit Description The DS3234 DS3234 real-time clock (RTC) can be interfaced to a microcontroller (µC) or digital signal processor (DSP) unit using an SPI-compatible interface. This application note shows how to connect a DS3234 DS3234 to a Motorola DSP that has a built-in SPI module. This circuit uses the Motorola DSP56F800DEMO DSP56F800DEMO Demonstration Board and CodeWarriorTM integrated development environment (IDE). Figure 1 illustrates the pin configuration of the DS3234 DS3234. Figure 1. The pin configuration of the DS3234 DS3234. Note that all N.C. pins must be connected to ground. Using the Example Software The example software was developed by starting with a blank project. Follow the instructions in the Motorola Kit Installation Guide (Tutorial: Creating a CodeWarrior Project), and, then, add the code included in this application note in DS3234 DS3234.c. Page 1 of 11 Operation The program uses a GPIO port to control the active-low CS pin on the DS3234 DS3234. Another GPIO port is used to monitor the active-low INT/SQW pin. The software initializes the SPI and SCI controller modules in the DSP. The DS3234 DS3234 supports SPI Modes 1 and 3. The SCI interface is used to provide program control on a terminal via an RS-232 RS-232 interface. The following six user-selected routines are provided: Write user-entered time and date values to the RTC, read the time and date, read SRAM, write SRAM, read the temperature, and read ten times using the active-low INT/SQW output in once-per-second alarm mode. Figure 2 shows a schematic of the circuit. This circuit comprises a daughter card that is attached to the Motorola Demonstration Board. Please note that the circuit in Figure 2 includes several RTCs with SPI buses. Only one RTC may be used at a time, and the software only supports the DS3234 DS3234. More detailed image (PDF, 138kB) Figure 2. This schematic illustrates the connections for interfacing the DS3234 DS3234 and other RTCs with SPI buses to a Motorola DSP. The example software code for interfacing a DS3234 DS3234 SPI-bus RTC to a Motorola DSP is as follows: /* File: DS3234 DS3234.c */ /* This example program was developed using the Motorola 56F800 56F800 Demo Board Kit. Follow the kit instalation guide for creating a CodeWarrior Project. Use the shell of the new project for this example. Note: This program is for example only and is not supported by Maxim. */ #include #include #include #include #include "port.h" "stdio.h" "stdlib.h" "appconfig.h" "string.h" /* * Main program for use with Embedded SDK */ void reset_spi(void); void wbyte_spi(unsigned char); void init_sci0(Word16); void tx_sci0(unsigned char); unsigned char rx_sci0(); Page 2 of 11 UWord16 input_data(void); void output_data(unsigned char *); void bcd2ascii(unsigned char); void int2ascii(unsigned char); unsigned char rbyte_spi(void); void init_3234(void); void rd_rtc(void); void rd_ram(void); void wr_ram(void); void rd_temp(void); void init_alarm(void); void loop_rd(void); unsigned char min, sec, hr, dow, date, mon, yr; #define #define #define #define #define REG_BASE 0x0000 SCI0_BASE 0x0F00 SPI_BASE 0x0F20 GPIOA_BASE 0x0FB0 GPIOB_BASE 0x0FC0 #define #define #define #define SCI0_SCIBR SCI0_SCICR SCI0_SCISR SCI0_SCIDR #define #define #define #define SPSCR SPDSR SPDRR SPDTR #define #define #define #define GPIO_A_PUR *(volatile UWord16 *)(GPIOA_BASE + 0) GPIO_A_DR *(volatile UWord16 *)(GPIOA_BASE + 1) GPIO_A_DDR *(volatile UWord16 *)(GPIOA_BASE + 2) GPIO_A_PER *(volatile UWord16 *)(GPIOA_BASE + 3) #define #define #define #define GPIO_B_PUR *(volatile UWord16 *)(GPIOB_BASE + 0) GPIO_B_DR *(volatile UWord16 *)(GPIOB_BASE + 1) GPIO_B_DDR *(volatile UWord16 *)(GPIOB_BASE + 2) GPIO_B_PER *(volatile UWord16 *)(GPIOB_BASE + 3) *(volatile *(volatile *(volatile *(volatile *(volatile *(volatile *(volatile *(volatile UWord16 UWord16 UWord16 UWord16 UWord16 UWord16 UWord16 UWord16 *)(SCI0_BASE *)(SCI0_BASE *)(SCI0_BASE *)(SCI0_BASE *)(SPI_BASE *)(SPI_BASE *)(SPI_BASE *)(SPI_BASE + + + + + + + + 0) 1) 2) 3) 0) 1) 2) 3) void main (void) { unsigned char val; reset_spi(); init_sci0(195); // 30MHz / 195 = 9600 baud GPIO_B_DR = 0x0008; // disable RTC - CS high GPIO_B_DR = 0; wbyte_spi(0x8e); rbyte_spi(); wbyte_spi(0x18); rbyte_spi(); // // // // GPIO_B_DR = 0x0008; // disable RTC - CS high enable RTC - CS low control register write address dummy read enable osc, 8kHz on INTb/SQW while(1) { output_data("\n\rDS3234 build: \0"); Page 3 of 11 output_data(_DATE_); output_data("\n\rR)ead RTC W)rite RTC\0"); output_data("\n\rT)emp rd L)oop rd w/INTb\0"); output_data("\n\rE)xt RAM rd wrI)te RAM\0"); output_data("\n\rEnter command: \0"); val = rx_sci0(); switch(val) { case 'E': case 'e': rd_ram(); break; case 'I': case 'i': wr_ram(); break; case 'L': case 'l': loop_rd(); break; case 'R': case 'r': rd_rtc(); break; case 'T': case 't': rd_temp(); break; case 'W': case 'w': init_3234(); break; } } return; } //SPSCR //15 14 13 12 // r MSB SPRF ERRIE 11 10 9 8 7 ovrf modf spte modfen spr1 6 spr0 5 4 sprie spmstr 3 2 1 cpol cpha spe 0 spite void reset_spi() { int val; SPSCR = 0x0056; // SPR0, SPMSTR, CPHA, SPE SPDSR = 0x0007; // 8-bit size SPSCR &= 0xfffd; SPSCR |= 0x0002; // clear spe, resets SPI (partial) // set spe, new values take effect GPIO_B_PER = 0x00f3; GPIO_B_DDR = 0x0009; // use GPIOB3 as CS for RTC, GPIOB2 as input // direction is output for CS GPIO_A_PER = 0x00f9; GPIO_A_DDR = 0x0006; GPIO_A_DR = 0; // enable/disable per function (1=enable) // direction is output (1=output) // write bits low (0=low) } void { wbyte_spi( unsigned char wbyte) while (!(SPSCR & 0x0200); // - write one byte -// wait for transmitter empty flag SPDTR = wbyte; } Page 4 of 11 void { bcd2ascii(unsigned char dat) // - convert bcd to ascii and send to sci - if( (dat >> 4) > 9) tx_sci0( (dat >> 4) + 0x37); else tx_sci0( (dat >> 4) + 0x30); // A - F // 0 - 9 if( (dat & 0x0f) > 9) tx_sci0( (dat & 0x0f) + 0x37); else tx_sci0( (dat & 0x0f) + 0x30); } void int2ascii(unsigned char dat) { unsigned char tmp1; // - convert int to ascii and send to sci - if(dat > 99) { tmp1 = (dat / 100) + 0x30; // if > 100, convert to ASCII 1 tx_sci0(tmp1); dat -= (100 * (int) (dat / 100) ); // adjust number } if(dat > 9) { tmp1 = (dat / 10) + 0x30; // if > 10, convert to ASCII 1 tx_sci0(tmp1); dat -= (10 * (int) (dat / 10) ); // adjust number } tmp1 = (dat) + 0x30; tx_sci0(tmp1); // convert to ASCII 1 } unsigned char rbyte_spi(void) // - read one byte -{ while (!(SPSCR & 0x2000); // wait for receiver full flag return(SPDRR); } void { init_sci0(Word16 baud) // - initialize SCI0 for RS232 RS232 comm - GPIO_B_PER = 0x00f3; GPIO_B_DDR = 0x0009; // set up // direction is output SCI0_SCIBR = baud; SCI0_SCICR = 0x2000; // baud rate // control reg } void tx_sci0(unsigned char val) // - transmit one char from SCI -{ UWord16 dat; SCI0_SCICR &= 0x3ffb; // turn SCI0_SCICR |= 8; while(!(SCI0_SCISR & 0x8000); while(!(SCI0_SCISR & 0x4000); receiver off // turn transmitter on // wait until TDRE is false // wait until TIDLE is false SCI0_SCIDR = (Word16) (val); while(!(SCI0_SCISR & 0x8000); while(!(SCI0_SCISR & 0x4000); // wait until TDRE is false // wait until TIDLE is false Page 5 of 11 SCI0_SCICR &= 0x3ff0; // turn transmitter off } unsigned char rx_sci0() // - receive one char to SCI -{ SCI0_SCICR &= 0x3ff0; // turn transmitter off SCI0_SCICR |= 4; // turn receiver on while(!(SCI0_SCISR & 0x2000); SCI0_SCICR &= 0x3ffb; // wait until RDRF is true // turn receiver off return( (unsigned char) (SCI0_SCIDR & 0x00FF) ); } UWord16 input_data() // - get string -{ UWord16 dat = 0, tmp[2] = {0,0}; while(1) { dat = (rx_sci0() & 0x00ff); // get a character if(dat = 0x0d) { tmp[0] = (tmp[0] & 0x000f); // convert ASCII 0-9 tmp[1] = (tmp[1] & 0x000f); // to 'BCD' dat = (tmp[1]