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Sam
Joined: 05 Feb 2008
Posts: 1
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| SPI for PIC18f4520 |
 Posted: Tue Feb 05, 2008 11:00 pm |
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We're trying to hook up two PICs through SPI.
We've connected:
MASTER RC5 --> SlAVE RC4
MASTER RC4 --> SLAVE RC4
MASTER CLK (PIN RC3, SCK)--> SLAVE CLK
SLAVE SELECT --> logic low (so that PIC2 is always the slave)
our initial code for MASTER:
| Code: | #include <18f4520.h>
#device high_ints=TRUE // this allows raised priority interrupts, which we need
#DEVICE ADC=10 // set ADC to 10 bit accuracy, or it could be just 8
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use spi(MASTER)
int value_send = 0;
int value_read = 0;
void main()
{
setup_spi(SPI_MASTER|SPI_H_TO_L|SPI_CLK_DIV_16);
While(TRUE){
spi_write(6);
output_d(6); // leds light up to show what it sent
value_read = spi_read(0);
}
} |
Our initial code for the SLAVE:
| Code: | #include <18f4520.h>
#device high_ints=TRUE // this allows raised priority interrupts, which we need
#DEVICE ADC=10 // set ADC to 10 bit accuracy, or it could be just 8
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use spi (SLAVE)
int recieve_buf = 0;
void main(void){
setup_spi(SPI_SLAVE | SPI_H_TO_L);
while(TRUE){
recieve_buf = 0;
if(spi_data_is_in())
recieve_buf = spi_read();
output_d(recieve_buf);
spi_write(0);
}
} |
Nothing is working. We can't get any communication going.
Thanks |
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Foppie
Joined: 16 Sep 2005
Posts: 138
Location: The Netherlands
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| Posted: Wed Feb 06, 2008 1:33 am |
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I think you should connect the Slave Select Pin to a output pin of the master. Then, when the master starts communication, the master should first take this pin low, and after that send the spi data and at last make the slave select pin high again.
The slave select pin is not used to define a device as slave (what is done in software), but to say that the slave is active. |
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