From 31a85397634222b867eb3e6b30c19052e7bb4eb7 Mon Sep 17 00:00:00 2001
From: Ivan Grokhotkov <igrokhotkov@gmail.com>
Date: Fri, 5 Dec 2014 00:05:01 +0300
Subject: [PATCH] Open-drain output mode

---
 cores/esp8266/Arduino.h                     |  1 +
 cores/esp8266/core_esp8266_wiring_digital.c | 11 ++++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/cores/esp8266/Arduino.h b/cores/esp8266/Arduino.h
index ea0917c5e..c7291dada 100644
--- a/cores/esp8266/Arduino.h
+++ b/cores/esp8266/Arduino.h
@@ -40,6 +40,7 @@ void yield(void);
 #define INPUT 0x0
 #define OUTPUT 0x1
 #define INPUT_PULLUP 0x2
+#define OUTPUT_OPEN_DRAIN 0x4
 
 #define PI 3.1415926535897932384626433832795
 #define HALF_PI 1.5707963267948966192313216916398
diff --git a/cores/esp8266/core_esp8266_wiring_digital.c b/cores/esp8266/core_esp8266_wiring_digital.c
index 0e075e56c..9db6f2f4e 100644
--- a/cores/esp8266/core_esp8266_wiring_digital.c
+++ b/cores/esp8266/core_esp8266_wiring_digital.c
@@ -88,11 +88,20 @@ void pinMode(uint8_t pin, uint8_t mode)
         gpio_output_set(0, 0, 0, 1 << pin);
         PIN_PULLUP_EN(mux);
     }
-    else
+    else if (mode == OUPUT)
     {
         gpio_output_set(0, 0, 1 << pin, 0);
     }
+    else if (mode == OUTPUT_OPEN_DRAIN)
+    {
+        GPIO_REG_WRITE(
+            GPIO_PIN_ADDR(GPIO_ID_PIN(pin)), 
+            GPIO_REG_READ(GPIO_PIN_ADDR(GPIO_ID_PIN(pin))) | 
+            GPIO_PIN_PAD_DRIVER_SET(GPIO_PAD_DRIVER_ENABLE)
+        );
 
+        GPIO_REG_WRITE(GPIO_ENABLE_ADDRESS, GPIO_REG_READ(GPIO_ENABLE_ADDRESS) | (1 << pin));
+    }
 }
 
 void digitalWrite(uint8_t pin, uint8_t val)