An arduino library to communicate using the Dallas one-wire protocol, where the Arduino takes the role of a slave. Implementation of a DS2413 on Arduino UNO and ATTINY85
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#include "Arduino.h"
#include "OneWireSlave.h"
// This is the pin that will be used for one-wire data (depending on your arduino model, you are limited to a few choices, because some pins don't have complete interrupt support)
// On Arduino Uno, you can use pin 2 or pin 3
Pin oneWireData(2);
Pin led(13);
// This is the ROM the arduino will respond to, make sure it doesn't conflict with another device
const byte owROM[7] = { 0x28, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02 };
// This sample emulates a DS18B20 device (temperature sensor), so we start by defining the available commands
const byte DS18B20_START_CONVERSION = 0x44;
const byte DS18B20_READ_SCRATCHPAD = 0xBE;
const byte DS18B20_WRITE_SCRATCHPAD = 0x4E;
// TODO:
// - handle configuration (resolution, alarms)
enum DeviceState
{
DS_WaitingReset,
DS_WaitingCommand,
DS_ConvertingTemperature,
DS_TemperatureConverted,
};
volatile DeviceState state = DS_WaitingReset;
// scratchpad, with the CRC byte at the end
volatile byte scratchpad[9];
volatile unsigned long conversionStartTime = 0;
// This function will be called each time the OneWire library has an event to notify (reset, error, byte received)
void owReceive(OneWireSlave::ReceiveEvent evt, byte data);
void setup()
{
led.outputMode();
led.writeLow();
// Setup the OneWire library
OWSlave.setReceiveCallback(&owReceive);
OWSlave.begin(owROM, oneWireData.getPinNumber());
}
void loop()
{
delay(10);
cli();//disable interrupts
// Be sure to not block interrupts for too long, OneWire timing is very tight for some operations. 1 or 2 microseconds (yes, microseconds, not milliseconds) can be too much depending on your master controller, but then it's equally unlikely that you block exactly at the moment where it matters.
// This can be mitigated by using error checking and retry in your high-level communication protocol. A good thing to do anyway.
DeviceState localState = state;
unsigned long localConversionStartTime = conversionStartTime;
sei();//enable interrupts
if (localState == DS_ConvertingTemperature && millis() > localConversionStartTime + 750)
{
float temperature = 42.0f; // here you could plug any logic you want to return the emulated temperature
int16_t raw = (int16_t)(temperature * 16.0f + 0.5f);
byte data[9];
data[0] = (byte)raw;
data[1] = (byte)(raw >> 8);
for (int i = 2; i < 8; ++i)
data[i] = 0;
data[8] = OWSlave.crc8(data, 8);
cli();
memcpy((void*)scratchpad, data, 9);
state = DS_TemperatureConverted;
OWSlave.beginWriteBit(1, true); // now that conversion is finished, start sending ones until reset
sei();
}
}
void owReceive(OneWireSlave::ReceiveEvent evt, byte data)
{
switch (evt)
{
case OneWireSlave::RE_Byte:
switch (state)
{
case DS_WaitingCommand:
switch (data)
{
case DS18B20_START_CONVERSION:
state = DS_ConvertingTemperature;
conversionStartTime = millis();
OWSlave.beginWriteBit(0, true); // send zeros as long as the conversion is not finished
break;
case DS18B20_READ_SCRATCHPAD:
state = DS_WaitingReset;
OWSlave.beginWrite((const byte*)scratchpad, 9, 0);
break;
case DS18B20_WRITE_SCRATCHPAD:
break;
}
break;
}
break;
case OneWireSlave::RE_Reset:
state = DS_WaitingCommand;
break;
case OneWireSlave::RE_Error:
state = DS_WaitingReset;
break;
}
}