From 7a3be851fa54e177e8d6b911b76df937a9daa295 Mon Sep 17 00:00:00 2001
From: Norman Gray <norman@astro.gla.ac.uk>
Date: Sun, 27 May 2018 12:29:50 +0100
Subject: [PATCH] Let pins float when writing (cf data sheet section 'write
 time slots')

---
 OneWire.cpp | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/OneWire.cpp b/OneWire.cpp
index 38bf4ee..805fa4f 100644
--- a/OneWire.cpp
+++ b/OneWire.cpp
@@ -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);
@@ -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);
 	}
@@ -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();