SPI with Atmega32 and At42QT2100 - c

Question

I have a problem to communicate from an Atmega3216PU to a at42qt2100.
The datasheets are: Atmega32PU16 and AT42QT2100
This is my code:
#include <avr/io.h>
#include <util/delay.h>
#include <stdio.h>
#define F_CPU 16000000
#define UART_BAUD_RATE 9600
#define UART_BAUD_REGISTERS (((F_CPU / (UART_BAUD_RATE * 16UL))) - 1)
int printCHAR(char character, FILE *stream)
{
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR = character;
return 0;
}
FILE uart_str = FDEV_SETUP_STREAM(printCHAR, NULL, _FDEV_SETUP_RW);
void setup(){
// Init SIO
UCSRB |= (1 << RXEN) | (1 << TXEN);
UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1);
UBRRL = UART_BAUD_REGISTERS;
fprintf(&uart_str, "");
stdout = &uart_str;
printf("");
//Init spi
//set MOSI, SCK and SS output, all others input
DDRB |= (1<<DDB7)|(1<<DDB5)|(1<<DDB4);
SPCR |= (1<<SPE)|(1<<MSTR)|(1<<SPR1)|(1<<SPR0)|(1<<CPHA)|(1<<CPOL);
}
void loop(){
uint8_t data = 0b01000000; //Sending this sequence should return device id
printf("Sending: %d \n",data);
_delay_ms(10000);
PORTB &= 0b11101111; // SS auf LOW!! (Pin4)
SPDR = data;
while(!(SPSR & (1<<SPIF)));
PORTB |= (1<<PB4); // SS auf HIGH!! (Pin4)
printf("Receiving: %d \n",SPDR);
_delay_ms(10000);
}
void main(){
setup();
while(1){
loop();
}
}
I should get an answer from the at42qt2100 with the device id 108 but i always get 0. This ist the output: Sending: 64 Receiving: 0
Does anybody see a misconfiguration?

Answer 1

I did a quick overview of the AT42QT2100 datasheet that you reference and I see a couple of problems right away:
After SS is set low, the host must wait >2us (in Free Run mode) before starting SCK. You are immediately initiating a SPI transfer and, if you are running a 16MHz, that means you may be starting the transmission as soon as 62.5ns after setting SS low.
The datasheet also says that the host must send 3 data bytes within 10ms or the transaction will be treated as an error and the communication exchange will be reset. You are sending 1 byte and then waiting 20s before sending the next byte.
The datasheet says that the device settings become active after the 3 bytes have been sent. That means that 3 more bytes must be sent to get the response to your command.
You should be doing something more along the lines of this:
#define NUM_DATA_BYTES 3
void loop(){
uint8_t sendData[NUM_DATA_BYTES] =
{
0b01000000, /* Device Version Command and default values. */
0b00000000, /* Default Value for Byte 2. */
0b11000000, /* Default Value for Byte 3. */
};
uint8_t receiveData[NUM_DATA_BYTES] = { 0 };
uint8_t i;
PORTB &= 0b11101111; // SS auf LOW!! (Pin4)
/* Ensure that >2us delay requirement is met. Although, the
for() loop below will probably introduce enough delay. */
_delay_ms(1);
/* Send command data. */
for (i = 0; i < NUM_DATA_BYTES; i++)
{
SPDR = sendData[i];
while(!(SPSR & (1<<SPIF)));
}
PORTB |= (1<<PB4); // SS auf HIGH!! (Pin4)
/* Delay here may be unnecessary, but it ensures that timing
issues do not occur. */
_delay_ms(1);
PORTB &= 0b11101111; // SS auf LOW!! (Pin4)
_delay_ms(1);
/* Receive device response data. */
for (i = 0; i < NUM_DATA_BYTES; i++)
{
SPDR = sendData[i];
while(!(SPSR & (1<<SPIF)));
receiveData[i] = SPDR;
printf("Receiving byte %d: %d \n", (i + 1), receiveData[i]);
}
PORTB |= (1<<PB4); // SS auf HIGH!! (Pin4)
_delay_ms(10000);
}
I am sure this code is not perfect, but it should help to get you on the right track. Good luck!