70 lines
2.5 KiB
C++
70 lines
2.5 KiB
C++
/* simulate one scan of a key martix, on open-drain active-low I/O expander
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BREADBOARD SETUP *******************************
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Teensy LC connected to MCP23018 I/O expander via I2C
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4.7k Ohm pullup resistors on SDA and SCL
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use volt meter to measure pin voltages
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MCP23018 has open-drain outputs (open-drain can only sink current)
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MCP23018 PIN DIAGRAM ***************************
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write port B read port A
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GND VSS 1 28 NC
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NC 2 27 GPA7
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jumper0 GPB0 3 26 GPA6
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GPB1 4 25 GPA5
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GPB2 5 24 GPA4 jumper4
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GPB3 6 23 GPA3
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jumper4 GPB4 7 22 GPA2
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GPB5 8 21 GPA1
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GPB6 9 20 GPA0 jumper0
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GPB7 10 19 INTA
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power VDD 11 18 INTB
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SCL SCL 12 17 NC
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SDA SDA 13 16 RESET power
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NC 14 15 ADDR GND
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*/
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#include "Wire.h"
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const uint8_t ADDR = 0x20; //MCP23018 I2C address with ADDR pin grounded
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void setup()
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{
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delay(1000); //time for Serial print to work
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// ================= configure ================
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Serial.print("config ");
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Wire.begin();
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Wire.beginTransmission(ADDR);
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Wire.write(0x01); //IODIRB Configure
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Wire.write(0); //as output
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Wire.endTransmission();
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Wire.beginTransmission(ADDR);
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Wire.write(0x00); //IODIRA Configuration
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Wire.write(~0); //as input
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Wire.endTransmission();
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Wire.beginTransmission(ADDR);
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Wire.write(0x0C); //GPPUA pull-up
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Wire.write(~0); //pull-up enabled
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Wire.endTransmission();
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// =================== scan ===================
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Serial.println("scan");
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Wire.beginTransmission(ADDR);
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Wire.write(0x13); //GPIOB output
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Wire.write(B00001111); //pins 0-3 off, pins 4-7 sink on (strobe, LED on)
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Wire.endTransmission();
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Wire.beginTransmission(ADDR);
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Wire.write(0x12); //GPIOA (immediately before requestFrom)
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Wire.endTransmission();
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Wire.requestFrom(ADDR, static_cast<uint8_t>(1)); //request one byte from GPIOA read
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Serial.print("portA=");
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Serial.println(Wire.read(), BIN); //prints portA=11101111
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}
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void loop() { }
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