Cannot make SPI work

[Meach]

Hello,

I am trying to use the SPI with MCP23S08 (IO Expander). I tried with Arduino before to make sure my code works and I read/write the correct registers but I cannot make it work with the RPI.

I connected the chip as follow:

• MOSI pin 19
• MISO pin 21
• SCLK pin 23
• CS pin 24

I also power the chip with +3.3V (pin 1)

Here is my code, can you spot something I am doing wrong?

SPI2 _spi;

//--------------------------------------------------------------
void ofApp::setup(){
    // Setup our chip on SPI 0
    _spi.setup("/dev/spidev0.0", 0, 1000000);

    // Configure chip: set all GPIO as input
    char data[3];
    data[0] = 0x40;     // Opcode
    data[1] = 0x00;     // IODIR - I/O Direction register
    data[2] = 0xff;     // all GPIO pins are inputs

    // Write the 3 data bits on channel 0
    _spi.readWrite(0, (unsigned char *)data, 3);
}

//--------------------------------------------------------------
void ofApp::update(){
    // Read all 8 IO expander inputs
    char data[3];
    data[0] = 0x41;     // Opcode
    data[1] = 0x09;     // GPIO - I/O port register address
    data[2] = 0x00;     // Dummy to read the value

    // Write the 3 data bits on channel 0
    val = _spi.readWrite(0, (unsigned char *)data, 3);

    ofLogVerbose() << "Val = " << val;
}

[kashimAstro]

Hi @Meach, sorry for delay.

right now i'm traveling for work, return to the lab this weekend, i keep you updated!

Ciao Dario

[Meach]

Hi @kashimAstro, Thanks for answer. I am using wiringPi now instead and managed to make it work. Also looking at the wiringPi documentation, I believe my problem is here:

// Write the 3 data bits on channel 0 val = _spi.readWrite(0, (unsigned char *)data, 3);

I expect the value read to be returned with readWrite function, where data variable might be overwritten with the read data.