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В представленных в И-те схемах используется разные варианты согласования уровней, а именно:
1. Резистор на питание(2кОм) +3,3 V (смысл мне не понятен т.к. на вход MMC все равно придет +5 от ПИКа)
2. Резистивный делитель (1,8к+3,3К)с выходв ПИКа (разве так можно при частоте SPI 5 МГЦ, фронты же завалены будут)
3. Прямое соединение, без каких-либо доп. элементов
Устройство не в серию, просто изучаю, поэтому вопрос: можно исп. п.3 или 1.
Есть еще вопрос по DAC c шиной I2S. обмен можно(нужно) вести просто по SPI? Но в ПИКе только один канал. Удасться ли выкрутиться за счет линий _CS, если и MMC и DAC посадить на единые линии SDO,CLK,SDI?
Может кто поделится своим куском кода инициализации (обмена) PIC-MMC на ASM. Хочу немного съэкономить времени. Или хотя бы асм-листинг C-программы, например вот этой:
/* PIC MMC Interface Test
http://www.captain.at/electronics/
Writes ASCII characters to the MMC, reads them back and sends the characters
to the linux machine via the serial port. Use "serterm" for testing:
# ./serterm
baud=9600
baud=9600
listening...
PIC online MMC online 0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcde
fghijklmno0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmno01
23456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmno0123456789:;<=
>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnoCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCC [more C's follow]
exiting...
Furthermore the PIC returns any character sent to it via the interrupt
service routine. Use "ser" for testing:
# ./ser
baud=9600
baud=9600
written:ABC
readport=ABC
#
Compile with CC5x: http://www.bknd.com/cc5x/
c:\picc\cc5x mmc.c -Ic:\picc\ -ammc.ASM -u
CC5x runs nicely on Linux with "dosemu" http://www.dosemu.org/
Credit:
SPI functions made by Michael Dworkin
http://home.wtal.de/Mischka/MMC/
*/
#include <16F876.h>
#include "int16CXX.H" // interrupt stuff
#define CP_off |= 0x3F30
#define LVP |= 128
#pragma config CP_off,PWRTE=on,WDTE=off,FOSC=HS,BODEN=on,LVP
#pragma bit CS @ PORTC.2 // output pin for chip select (MMC)
#pragma rambank 0
char sector1[64];
int currentrambank;
int counter;
#pragma rambank 1
char sector2[64];
#pragma rambank 2
char sector3[64];
#pragma rambank 3
char sector4[64];
#pragma origin 4 // force interrupt service routine at address 4
interrupt myInterrupt(void) // ISR
{
int_save_registers
char rec;
if (RCIF) // USART interrupt ?
{
while(!TXIF) { // wait for serial register to be sent, if there is still something in there
nop();
}
rec = RCREG; // Get the received character
TXREG = rec; // write to serial register -> start transmission
RCIF = 0; // clear USART int flag
}
int_restore_registers
}
void InitUSART()
{
PORTA = 0;
PORTB = 0;
PORTC = 0;
BRGH = 1; // high speed serial mode
SPBRG = 25; // Set 9600 baud for 4 MHz oscillator
SYNC = 0; // Clear SYNC bit -> Set ASYNC Mode
SPEN = 1; // Set serial port enable
TX9 = 0; // 8-bit transmissions
TXEN = 1; // Enable transmission
RCIE = 1; // Rx interrupts are desired
RX9 = 0; // 8-bit receptions
CREN = 1; // Enable reception
}
void initint() // init interrupts
{
GIE = 1; // Set Global Interrupt Enable
PEIE = 1; // Set Peripheral Interrupt Enable
}
void fillram() // fill RAM (sector1..4) with ASCII characters
{
int i;
int x;
for (i=0;i<=63;i++) {
x = i + 48;
sector1[i] = x;
sector2[i] = x;
sector3[i] = x;
sector4[i] = x;
}
}
char SPI(char d) // send character over SPI
{
SSPBUF = d; // send character
while (!BF); // wait until sent
return SSPBUF; // and return the received character
}
char Command(char befF,uns16 AdrH,uns16 AdrL,char befH )
{ // sends a command to the MMC
char a;
SPI(0xFF);
SPI(befF);
SPI(AdrH.high8);
SPI(AdrH.low8);
SPI(AdrL.high8);
SPI(AdrL.low8);
SPI(befH);
SPI(0xFF);
return SPI(0xFF); // return the last received character
}
bit MMC_Init() // init SPI
{
SMP = 0; // input is valid in the middle of clock
CKE = 0; // rising edge is data capture
CKP = 1; // high value is passive state
SSPM1 = 1; // speed f/64(312kHz), Master
SSPEN = 1; // enable SPI
CS = 1; // disable MMC
char i;
// start MMC in SPI mode
for(i=0; i < 10; i++)SPI(0xFF); // send 10*8=80 clock pulses
CS=0; // MMC-Enabled
if (Command(0x40,0,0,0x95) !=1) goto mmcerror; // Reset MMC
st: // if there is no MMC, prg. loops here
if (Command(0x41,0,0,0xFF) !=0) goto st;
return 1;
mmcerror:
return 0;
}
void serialterminate() { // terminate sent string!!!
while(!TXIF);
TXREG = 0x0d;
while(!TXIF);
TXREG = 0x0a;
}
void SerString(const char *str) // send string via RS232
{
char ps;
ps = *str; // pointer of start of string into ps
while(ps>0) // test if end of string is reached
{
str++; // set pointer to next char
if (ps== 0) break; // test if end of string is reached
while(!TXIF); // test if TXREG empty
TXREG = ps ; // send character
ps = *str; // content of pointer into ps
}
serialterminate();
}
bit writeramtommc() // write RAM (sector1..4) to MMC
{
// 512 byte-write-mode
if (Command(0x58,0,512,0xFF) !=0) {
SerString("MMC: write error 1 ");
return 1;
}
SPI(0xFF);
SPI(0xFF);
SPI(0xFE);
uns16 i;
// write ram sectors to MMC
for (i=0;i<=63;i++) {
SPI(sector1[i]);
}
for (i=0;i<=63;i++) {
SPI(sector2[i]);
}
for (i=0;i<=63;i++) {
SPI(sector3[i]);
}
for (i=0;i<=63;i++) {
SPI(sector4[i]);
}
for (i=0;i<256;i++) { // fill rest with 'C'
SPI('C');
}
SPI(255); // at the end, send 2 dummy bytes
SPI(255);
i = SPI(0xFF);
i &= 0b.0001.1111;
if (i != 0b.0000.0101) {
SerString("MMC: write error 2 ");
return 1;
}
while(SPI(0xFF) != 0xFF); // wait until MMC is not busy anymore
return 0;
}
bit sendmmc() // send 512 bytes from the MMC via the serial port
{
uns16 i;
// 512 byte-read-mode
if (Command(0x51,0,512,0xFF) !=0) {
SerString("MMC: read error 1 ");
return 1;
}
while(SPI(0xFF) != 0xFE); // wait for 0xFE - start of any transmission
for(i=0; i < 512; i++)
{
while(!TXIF); // wait until TXREG is empty
TXREG = SPI(0xFF); // get MMC byte and send via RS232
}
serialterminate();
SPI(0xFF); // at the end, send 2 dummy bytes
SPI(0xFF);
return 0;
}
void main(void)
{
InitUSART(); // initialize serial port
initint(); // initialize interrupts
ADCON1=0x6; // PortA Digital
// set ports for I/O
TRISC = 0b.1101.0011; // sck rc3-0, sdo rc5-0, CS rc2-0.
TRISB = 0b.0000.0010; // RB2>TX, RB1>RX
SerString("PIC online "); // start message
// SerString(0x00); // start message
// init MMC and send message if ok
if (MMC_Init()) SerString("MMC online ");
fillram(); // fill the RAM with ASCII characters
writeramtommc(); // write RAM to MMC
sendmmc(); // send 512 bytes of the MMC via serial port
while(1) {
nop();
nop();
}
}
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