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Let pins float when writing (cf data sheet section 'write time slots') #60

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Let pins float when writing (cf data sheet section 'write time slots') #60

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17 changes: 14 additions & 3 deletions OneWire.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -184,7 +184,7 @@ uint8_t OneWire::reset(void)
delayMicroseconds(480);
noInterrupts();
DIRECT_MODE_INPUT(reg, mask); // allow it to float
delayMicroseconds(70);
delayMicroseconds(70); // must be more than 60us, and less than (15+60)us
r = !DIRECT_READ(reg, mask);
interrupts();
delayMicroseconds(410);
Expand All @@ -201,19 +201,28 @@ void OneWire::write_bit(uint8_t v)
volatile IO_REG_TYPE *reg IO_REG_BASE_ATTR = baseReg;

if (v & 1) {
// Data sheet: To generate a Write 1 time slot, after
// pulling the 1-Wire bus low, the bus master must
// release the 1-Wire bus within 15us. When the bus is
// released, the 5kOhm pullup resistor will pull the
// bus high.
noInterrupts();
DIRECT_WRITE_LOW(reg, mask);
DIRECT_MODE_OUTPUT(reg, mask); // drive output low
delayMicroseconds(10);
DIRECT_WRITE_HIGH(reg, mask); // drive output high
DIRECT_MODE_INPUT(reg, mask); // release
interrupts();
delayMicroseconds(55);
} else {
// To generate a Write 0 time slot, after pulling the
// 1-Wire bus low, the bus master must continue to
// hold the bus low for the duration of the time slot
// (at least 60us).
noInterrupts();
DIRECT_WRITE_LOW(reg, mask);
DIRECT_MODE_OUTPUT(reg, mask); // drive output low
delayMicroseconds(65);
DIRECT_WRITE_HIGH(reg, mask); // drive output high
DIRECT_MODE_INPUT(reg, mask); // release
interrupts();
delayMicroseconds(5);
}
Expand All @@ -232,8 +241,10 @@ uint8_t OneWire::read_bit(void)
noInterrupts();
DIRECT_MODE_OUTPUT(reg, mask);
DIRECT_WRITE_LOW(reg, mask);
// must be low for minimum of 1us
delayMicroseconds(3);
DIRECT_MODE_INPUT(reg, mask); // let pin float, pull up will raise
// DS18B20 data is valid for 15us after falling edge
delayMicroseconds(10);
r = DIRECT_READ(reg, mask);
interrupts();
Expand Down