keybrd/src/Port_MCP23S17.cpp

#include "Port_MCP23S17.h"

/* transfer() writes data to registerAddr, reads portSate from registerAddr, and returns portState.

MCP23S17 SPI interface is 10 MHz max.
The electrical limitation to bus speed is bus capacitance and the length of the wires involved.
Longer wires require lower clock speeds.
*/
uint8_t Port_MCP23S17::transfer(const uint8_t command, const uint8_t registerAddr,
                                const uint8_t data)
{
    uint8_t portState;                          //bit pattern

    SPI.beginTransaction( SPISettings(5000000, MSBFIRST, SPI_MODE0) ); //control SPI bus, 5 MHz
    digitalWrite(SS, LOW);                      //enable Slave Select
    SPI.transfer(command);                      //write or read command
    SPI.transfer(registerAddr);                 //register address to write data to
    portState = SPI.transfer(data);             //write data, read portState
    digitalWrite(SS, HIGH);                     //disable Slave Select
    SPI.endTransaction();

    return portState;
}

/* beginProtocol() is called from Scanner_IOE::begin().  Initiates SPI bus.
*/
void Port_MCP23S17::beginProtocol()
{
    pinMode(SS, OUTPUT);                        //configure controller's Slave Select pin to output
    digitalWrite(SS, HIGH);                     //disable Slave Select
    SPI.begin();
}

/* begin() is called from Scanner_IOE::begin().
strobeOn is logic level of strobe on, HIGH or LOW
configure IODIR and GPPU.
*/
void Port_MCP23S17::begin(const uint8_t strobeOn)
{
    uint8_t pullUp;                             //bits, GPPU 0=pull-up disabled, 1=pull-up enabled

    if (strobeOn == LOW)                        //if active low
    {
        pullUp = readPins;              //0=pull-up disabled (for LED), 1=pull-up enabled (for read)
    }
    else                                        //if active high
    {
        pullUp = 0;                         //0=pull-up disabled (for external pull-down resistors)
    }

    transfer(deviceAddr << 1, portNum, readPins); //configure IODIR
    transfer(deviceAddr << 1, portNum + 0x0C, pullUp); //configure GPPU
}

/* setLow() sets pin output LOW.
pin is bit pattern, where pin being set is 1.
*/
void Port_MCP23S17::setLow(const uint8_t pin)
{
    outputVal &= ~pin;                 //set pin output to low
    transfer(deviceAddr << 1, portNum + 0x12, outputVal); //set GPIO port to outputVal
}

/* setHigh() sets pin output HIGH.
pin is bit pattern, where pin being set is 1.
*/
void Port_MCP23S17::setHigh(const uint8_t pin)
{
    outputVal |= pin;                  //set pin output to high
    transfer(deviceAddr << 1, portNum + 0x12, outputVal); //set GPIO port to outputVal
}

/* read() returns portState.  Only portState pins with pull resistors are valid.
*/
uint8_t Port_MCP23S17::read()
{
    return transfer( (deviceAddr << 1) | 1, portNum + 0x12, 0); //read from GPIO
}