本應用筆記提供了用于將串行外設接口（SPI）RTC與內(nèi)置SPI接口模塊的摩托羅拉DSP連接的硬件和軟件示例。本示例使用摩托羅拉DSP演示套件作為電路的基礎(chǔ)。

DS1306引腳配置

引腳配置

描述

DS1306實時時鐘（RTC）可通過3線或SPI?接口與微控制器（μC）或數(shù)字信號處理（DSP）單元連接。本應用筆記介紹了如何將DS1306連接至內(nèi)置SPI接口模塊的摩托羅拉DSP。DS1305也可用于此應用。該電路使用摩托羅拉DSP56F800DEMO演示板和CodeWarrior IDE。

使用示例軟件

示例軟件是從空白項目開始開發(fā)的。按照摩托羅拉套件安裝指南（教程：創(chuàng)建 CodeWarrior 項目）中的說明進行操作，了解詳細信息。在main.c中添加本應用筆記中包含的代碼。

操作

該程序使用GPIO端口來控制DS1306上的CE。軟件初始化DSP中的SPI控制器模塊，將時間和日期寫入DS1306。然后，軟件循環(huán)讀取時間和日期。DS1305和DS1306支持SPI模式1和3。

圖1所示為該電路的原理圖。該電路包括連接到摩托羅拉演示板的子卡。請注意，圖1中的電路包括幾個帶SPI接口的RTC。一次只能使用一個RTC，軟件僅支持DS1306。該軟件如圖2所示。

圖 1.DSP56F800演示板的子卡。

圖2.演示代碼。

/* File: main.c */
/* This example program was developed using the Motorola
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 Dallas Semiconductor
Maxim. */

#include "port.h"
#include "stdio.h"
#include "stdlib.h"

/*******************************************************
* Main program for use with Embedded SDK
*******************************************************/

extern sampleASM (void);

void reset_spi(void);
void wbyte_spi(unsigned char);
unsigned char rbyte_spi(void);

#define      REG_BASE 0x0000
#define      SPI_BASE 0x0F20
#define      GPIOB_BASE 0x0FC0

#define      SPSCR *(volatile UWord16 *)(SPI_BASE + 0)
#define      SPDSR *(volatile UWord16 *)(SPI_BASE + 1)
#define      SPDRR *(volatile UWord16 *)(SPI_BASE + 2)
#define      SPDTR *(volatile UWord16 *)(SPI_BASE + 3)

#define      GPIO_B_PUR *(volatile UWord16 *)(GPIOB_BASE + 0)
#define      GPIO_B_DR *(volatile UWord16 *)(GPIOB_BASE + 1)
#define      GPIO_B_DDR *(volatile UWord16 *)(GPIOB_BASE + 2)
#define      GPIO_B_PER *(volatile UWord16 *)(GPIOB_BASE + 3)

void main (void)
{
unsigned char      min=0x58, sec=0x59, hr=0x09, dow=0x04, date=0x23,
                         mon=0x10, yr=0x03;

      reset_spi();

      GPIO_B_DR = 0;              // disble RTC - CS low

      GPIO_B_DR = 0x0008;         // enable RTC - CS high
      wbyte_spi(0x8f);            // control register write address
      rbyte_spi();                // dummy read
      wbyte_spi(0);               // disable write protect
      rbyte_spi();
      GPIO_B_DR = 0;              // disble RTC - CS low

      GPIO_B_DR = 0x0008;         // enable RTC - CS high
      wbyte_spi(0x80);            // select seconds register write address
      rbyte_spi();                // dummy read
      wbyte_spi(sec);             // seconds register data

      rbyte_spi();
      wbyte_spi(min);             // minutes register
      rbyte_spi();
      wbyte_spi(hr);              // hours register
      rbyte_spi();
      wbyte_spi(dow);             // day of week register
      rbyte_spi();
      wbyte_spi(date);            // date register
      rbyte_spi();
      wbyte_spi(mon);             // month register
      rbyte_spi();
      wbyte_spi(yr);              // year register
      rbyte_spi();
      GPIO_B_DR = 0;              // disble RTC - CS low

      while(1)
      {
             GPIO_B_DR = 0x0008;         // enable RTC - CS high
             wbyte_spi(0);               // seconds register read address
             rbyte_spi();                // dummy read
             wbyte_spi(0);
             sec = rbyte_spi();          // read seconds register
             wbyte_spi(0);
             min = rbyte_spi();          // ditto minutes
             wbyte_spi(0);
             hr = rbyte_spi();           // and so on
             wbyte_spi(0);
             dow = rbyte_spi();
             wbyte_spi(0);
             date = rbyte_spi();
             wbyte_spi(0);
             mon = rbyte_spi();
             wbyte_spi(0);
             yr = rbyte_spi();

             GPIO_B_DR = 0; // disable RTC - CS low
      }
      return;
}

//SPSCR
//15  14  13  12  11  10  9  8  7  6  5  4  3  2  1
0
// r MSB SPRF ERRIE  ovrf modf spte modfen spr1    spr0    sprie spmstr    cpol cpha
spe  spite

void reset_spi()
{
int   val;
      SPSCR = 0x0096;             // SPR0, SPMSTR, CPHA, SPE
      SPDSR = 0x0007;             // 8-bit size

      SPSCR &= 0xfffd;            // clear spe, resets SPI (partial)
      SPSCR |= 0x0002;            // set spe, new values take effect

      GPIO_B_PER = 0x00f3;        // use GPIOB3 as CS for RTC
      GPIO_B_DDR = 0x000c;        // direction is output
}

void wbyte_spi( unsigned char wbyte)     // ------ write one byte -------
{
      while (!(SPSCR & 0x0200));         // wait for transmitter empty flag

      SPDTR = wbyte;
}

unsigned char rbyte_spi(void)            // -------- read one byte ----------
{
      while (!(SPSCR & 0x2000));         // wait for receiver full flag

      return(SPDRR);
}

審核編輯：郭婷