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