Ok I've solved it, as least as far as I need to. The code below rewrites the EEPROM location for the slave address and tries all possible CRC bytes until it finds the correct one. Be sure to cycle the power to the MLX after writing to it, or you get strange results.
I'm not sure what the second address config byte does, but for my purposes an address in the first location and a zero in the second seemed to work.
#include <i2cmaster.h>
// Pins: Standard: SDA:A4 SCL:A5
// Mega: SDA:D20 SCL:D21
byte MLXAddr = 0x5A<<1; // Default address
//byte MLXAddr = 0; // Universal address
void setup(){
Serial.begin(9600);
Serial.println("Setup...");
i2c_init(); //Initialise the i2c bus
PORTC = (1 << PORTC4) | (1 << PORTC5); //enable pullups
delay(5000); // Wait to allow serial connection
ReadAddr(0); // Read current address bytes
ChangeAddr(0x55, 0x00); // Change address to new value
//ChangeAddr(0x5A, 0xBE); // Change address to default value
ReadAddr(0); // Read address bytes
delay(5000); // Cycle power to MLX during this pause
ReadTemp(0); // Read temperature using default address
ReadTemp(MLXAddr); // Read temperature using new address
}
void loop(){
delay(1000); // wait a second
}
word ChangeAddr(byte NewAddr1, byte NewAddr2) {
Serial.println("> Change address");
i2c_start_wait(0 + I2C_WRITE); //send start condition and write bit
i2c_write(0x2E); //send command for device to return address
i2c_write(0x00); // send low byte zero to erase
i2c_write(0x00); //send high byte zero to erase
if (i2c_write(0x6F) == 0) {
i2c_stop(); //Release bus, end transaction
Serial.println(" Data erased.");
}
else {
i2c_stop(); //Release bus, end transaction
Serial.println(" Failed to erase data");
return -1;
}
Serial.print(" Writing data: ");
Serial.print(NewAddr1, HEX);
Serial.print(", ");
Serial.println(NewAddr2, HEX);
for (int a = 0; a != 256; a++) {
i2c_start_wait(0 + I2C_WRITE); //send start condition and write bit
i2c_write(0x2E); //send command for device to return address
i2c_write(NewAddr1); // send low byte zero to erase
i2c_write(NewAddr2); //send high byte zero to erase
if (i2c_write(a) == 0) {
i2c_stop(); //Release bus, end transaction
delay(100); // then wait 10ms
Serial.print("Found correct CRC: 0x");
Serial.println(a, HEX);
return a;
}
}
i2c_stop(); //Release bus, end transaction
Serial.println("Correct CRC not found");
return -1;
}
void ReadAddr(byte Address) {
Serial.println("> Read address");
Serial.print(" MLX address: ");
Serial.print(Address, HEX);
Serial.print(", Data: ");
i2c_start_wait(Address + I2C_WRITE); //send start condition and write bit
i2c_write(0x2E); //send command for device to return address
i2c_rep_start(Address + I2C_READ);
Serial.print(i2c_readAck(), HEX); //Read 1 byte and then send ack
Serial.print(", ");
Serial.print(i2c_readAck(), HEX); //Read 1 byte and then send ack
Serial.print(", ");
Serial.println(i2c_readNak(), HEX);
i2c_stop();
}
float ReadTemp(byte Address) {
int data_low = 0;
int data_high = 0;
int pec = 0;
Serial.println("> Read temperature");
Serial.print(" MLX address: ");
Serial.print(Address, HEX);
Serial.print(", ");
i2c_start_wait(Address + I2C_WRITE);
i2c_write(0x07); // Address of temp bytes
// read
i2c_rep_start(Address + I2C_READ);
data_low = i2c_readAck(); //Read 1 byte and then send ack
data_high = i2c_readAck(); //Read 1 byte and then send ack
pec = i2c_readNak();
i2c_stop();
//This converts high and low bytes together and processes temperature, MSB is a error bit and is ignored for temps
float Temperature = 0x0000; // zero out the data
// This masks off the error bit of the high byte, then moves it left 8 bits and adds the low byte.
Temperature = (float)(((data_high & 0x007F) << 8) + data_low);
Temperature = (Temperature * 0.02) - 273.16;
Serial.print(Temperature);
Serial.println(" C");
return Temperature;
}