PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Mon May 01, 2006 12:54 am |
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| Quote: | | Does anyone have a sample code of a WORKING Interrupt based SPI Slave? |
Here is a demo program. This program takes characters that
are typed in on the PC's keyboard and sends them out via
software SPI to the interrupt-driven SPI slave, where they are
stored in a buffer. The characters are then read from the
buffer and sent back to the PC, where they are displayed in
a terminal window.
In a real implementation, there would be two separate boards
and you would likely use hardware SPI in the Master board.
I had to use a software Master for this demo because it's
all done in one PIC, and the PIC only has one hardware SSP
module.
| Code: |
// This program demonstrates an SPI slave with the PicDem2-Plus
// board. Both Master and Slave are contained in one 16F877
// chip. The Slave uses the hardware SPI pins on Port C and
// Port A. The Master uses software SPI on Port B.
// See the following website for an explanation of SPI modes.
// http://www.totalphase.com/support/articles/article03/
#include <16F877.H>
#device *=16
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
// Software SPI pins used by Master.
#define MASTER_SS PIN_B2 // Connect to Slave \SS (Pin A5)
#define MASTER_SCK PIN_B3 // Connect to Slave SCK (Pin C3)
#define MASTER_SDI PIN_B4 // Connect to Slave SDO (Pin C5)
#define MASTER_SDO PIN_B5 // Connect to Slave SDI (Pin C4)
// Use Charlie U's SPI mode definitions.
#define SPI_MODE_0_0 0x4000
#define SPI_MODE_0_1 0x0000
#define SPI_MODE_1_0 0x0010
#define SPI_MODE_1_1 0x4010
// Variables used for the SPI slave receive buffer.
#define BUFFER_SIZE 80
int8 buffer[BUFFER_SIZE];
int8 next_in = 0;
int8 next_out = 0;
#define spi_kbhit (next_in != next_out)
//----------------------------
// Create an interrupt-driven SPI receive
// buffer, similar to the way it's done for
// RS-232 in the CCS example file, EX_SISR.C.
#int_ssp
void ssp_isr(void)
{
buffer[next_in] = spi_read();
next_in++;
if(next_in >= BUFFER_SIZE)
next_in = 0;
}
//----------------------------
// Wait for a character to become available
// in the spi slave's receive buffer. Then
// get it from the buffer and return it.
int8 spi_bgetc(void)
{
int8 c;
while(!spi_kbhit);
c = buffer[next_out];
next_out++;
if(next_out >= BUFFER_SIZE)
next_out = 0;
return(c);
}
//----------------------------
// Transmit a byte via the software SPI port.
// Use SPI mode 0,0.
void master_spi_write(char data)
{
int8 i;
disable_interrupts(GLOBAL);
output_low(MASTER_SS);
for(i = 0; i < 8; i++)
{
if(bit_test(data, 7))
output_high(MASTER_SDO);
else
output_low(MASTER_SDO);
delay_us(5);
output_high(MASTER_SCK);
delay_us(5);
output_low(MASTER_SCK);
data <<= 1;
}
output_high(MASTER_SS);
enable_interrupts(GLOBAL);
}
//======================================
void main()
{
char c;
// Initialize the hardware SSP for SPI Slave mode.
setup_spi(SPI_SLAVE | SPI_MODE_0_0);
// Initialize the software Master SPI pins.
output_high(MASTER_SS);
output_low(MASTER_SCK);
output_low(MASTER_SDO);
output_float(MASTER_SDI);
// Enable interrupts for the SPI slave.
clear_interrupt(INT_SSP);
enable_interrupts(INT_SSP);
enable_interrupts(GLOBAL);
// If the user presses a key on the PC, get the
// character and send it out the software SPI
// master port. Then when the character is
// received by the hardware SPI slave and placed
// in its buffer, get it and send it back to the PC.
while(1)
{
if(kbhit()) // Char available from PC ?
{
c = getc(); // If so, get it
master_spi_write(c); // Send it via SPI
}
if(spi_kbhit) // Char available from SPI slave ?
{
c = spi_bgetc(); // If so, get it
putc(c); // Send it to the PC
}
}
} |
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