SPI RTC与摩托罗拉DSP接口

本应用笔记提供了用于将串行外设接口（SPI）RTC与内置SPI接口模块的摩托罗拉DSP连接的硬件和软件示例。本示例使用摩托罗拉DSP演示套件作为电路的基础。

DS1306引脚配置

引脚配置

描述

DS1306实时时钟（RTC）可通过3线或SPI™接口与微控制器（μC）或数字信号处理（DSP）单元连接。本应用笔记介绍了如何将DS1306连接至内置SPI接口模块的摩托罗拉DSP。DS1305也可用于此应用。该电路使用摩托罗拉DSP56F800DEMO演示板和CodeWarrior IDE。

使用示例软件

示例软件是从空白项目开始开发的。按照摩托罗拉套件安装指南（教程：创建 CodeWarrior 项目）中的说明进行操作，了解详细信息。在main.c中添加本应用笔记中包含的代码。

操作

该程序使用GPIO端口来控制DS1306上的CE。软件初始化DSP中的SPI控制器模块，将时间和日期写入DS1306。然后，软件循环读取时间和日期。DS1305和DS1306支持SPI模式1和3。

图1所示为该电路的原理图。该电路包括连接到摩托罗拉演示板的子卡。请注意，图1中的电路包括几个带SPI接口的RTC。一次只能使用一个RTC，软件仅支持DS1306。该软件如图2所示。

图 1.DSP56F800演示板的子卡。

图2.演示代码。

/* 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);
}

审核编辑：郭婷