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keybrd/unit_tests/MCP23S17_read/MCP23S17_read.ino

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2016-09-01 02:29:59 +00:00
/* this works
The setup is an MCP23S17 I/O expander on a Teensy LC controller.
MCP23S17 port B pins are alternately grounded and energized.
portBState is a bitwise reading of port B.
output is: 10101010
posted on http://arduino.stackexchange.com/questions/tagged/spi
http://arduino.stackexchange.com/questions/28792/reading-an-mcp23s17-i-o-expander-port-with-the-arduino-spi-library
*/
#include <SPI.h>
const uint8_t ADDR = 0x20; //MCP23S17 address, all 3 ADDR pins are grounded
const uint8_t OPCODE_READ = (ADDR << 1 | 0x01); //MCP23S17 opcode read has LSB set
const uint8_t IODIRB = 0x01;
const uint8_t GPIOB = 0x13;
uint8_t portBState = 0; //bit wise
void setup()
{
Serial.begin(9600);
delay(1000);
pinMode(SS, OUTPUT); //configure controller's Slave Select pin to output
digitalWrite(SS, HIGH); //disable Slave Select
SPI.begin();
//IODIRB register is already configured to input by default
SPI.beginTransaction(SPISettings (SPI_CLOCK_DIV8, MSBFIRST, SPI_MODE0)); //gain control of SPI bus
digitalWrite(SS, LOW); //enable Slave Select
SPI.transfer(OPCODE_READ); //read command
SPI.transfer(GPIOB); //register address to read data from
portBState = SPI.transfer(0); //save the data (0 is dummy data to send)
digitalWrite(SS, HIGH); //disable Slave Select
SPI.endTransaction(); //release the SPI bus
Serial.println(portBState, BIN); //should print 10101010
}
void loop() { }