chap9.c

Motorola 6812芯片开发的接口程序。

// Chapter 9 6812 C programs
// Jonathan W. Valvano
// This software accompanies the book,
// Embedded Microcomputer Systems: Real Time Interfacing
// published by Brooks Cole, 1999

// Program 9.1. Software to configure the chip select for the external PROM.
void PROMinit(void){
	CSSTR0=(CSSTR0&0xF3)|0x08;} // 2 cycle stretch on CSP0

// Program 9.2. Software to configure the chip select for the external RAM.
void RAMinit(void){
	MODE=0x3B			// special expanded narrow mode
	PEAR=0x2C;			// enable E, R/W, LSTRB(not needed)
	WINDEF=WINDEF&0x7F;		// disable DPAGE
	CSCTL0=CSCTL0|0x10;		// enable CSD
	CSCTL1=CSCTL1|0x10;		// CSD $0000 to $7FFF
	CSSTR0=(CSSTR0&0xFC)|0x01;}	// 1 cycle stretch on CSD

// Program 9.3. Software to configure the mode for the external RAM.
void RAMinit(void){
	MODE=0x39				// special expanded narrow mode
	MISC=(MISC&0xF3)|0x08;		// 2 cycle stretch on external
	PEAR=0x2C;}				// enable DBE, E, R/W, LSTRB(not needed)

// Program 9.4. Software to configure the chip select for the external PROM.
void PROMinit(void){
	CSSTR0=(CSSTR0&0xF3)|0x04;} // 1 cycle stretch on CSP0

//  Program 9.5. Software to configure the chip select for the external RAM.
void RAMinit(void){
	MODE=0x7B			// special expanded wide mode
	PEAR=0x2C;			// enable E, R/W, LSTRB
	WINDEF=WINDEF&0x7F;		// disable DPAGE
	CSCTL0=CSCTL0|0x10;		// enable CSD
	CSCTL1=CSCTL1|0x10;		// CSD $0000 to $7FFF
	CSSTR0=(CSSTR0&0xFC)|0x01;}	// 1 cycle stretch on CSD

//  Program 9.6. Software to configure the mode for the external RAM.
void RAMinit(void){
	MODE=0x79				// special expanded wide mode
	MISC=(MISC&0xF3)|0x08;		// 2 cycle stretch on external
	PEAR=0x2C;}				// enable DBE, E, R/W, LSTRB

//  Program 9.7. Software to configure the mode for the extended RAM.
void RAMinit(void){
	MODE=0x7B			// special expanded wide mode
	PEAR=0x2C;			// enable E, R/W, LSTRB
	WINDEF=WINDEF|0x80;		// enable DPAGE
	MXAR=0x03;			// enable A17, A16 on Port G
	CSCTL0=CSCTL0|0x10;		// enable CSD
	CSCTL1=CSCTL1&0xEF;		// CSD $7000 to $7FFF
	CSSTR0=(CSSTR0&0xFC)|0x01;}	// 1 cycle stretch on CSD

//  Program 9.8. Method for accessing extended RAM.
struct addr20
{   unsigned char msb;    // bits 19-12, only 17-12 used in this interface
    unsigned int lsw;     // bits 11-0
};
typedef struct addr20 addr20Type;
char ReadMem(addr20Type addr){ char *pt;
	DPAGE=addr.msb;			// set address bits 19-12, only 17-12 used
	pt=(char *)(0x7000+addr.lsw);	// set address bits 11-0
	return *pt;}			// read access
void WriteMem(addr20Type addr, char data){ char *pt;
	DPAGE=addr.msb;			// set address bits 19-12, only 17-12 used
	pt=(char *)(0x7000+addr.lsw);	// set address bits 11-0
	*pt=data;}				// write access

//  Program 9.9. Software to configure the mode for the extended PROM.
void PROMinit(void){
	MODE=0x7B			// special expanded wide mode
	PEAR=0x2C;			// enable E, R/W, LSTRB (none needed)
	WINDEF=WINDEF|0x40;		// enable PPAGE
	MXAR=0x01F;			// enable A20-A16 on Port G
	CSSTR0=(CSSTR0&0xF3)|0x04;}	// 1 cycle stretch on CSP0

//  Program 9.10. Method for accessing extended PROM.
struct addr22
{   unsigned char msb;    // bits 21-14, only 20-14 used in this interface
    unsigned int lsw;     // bits 13-0
};
typedef struct addr22 addr22Type;
char ReadPROM(addr22Type addr){ char *pt;
	PPAGE=addr.msb;			// set address bits 21-14
	pt=(char *)(0x8000+addr.lsw);	// set address bits 13-0
	return *pt;}				// read access