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--- esp8266:how-to-use-all-esp01-gpio-pins [2024/11/22 12:02] – external edit 127.0.0.1
+++ esp8266:how-to-use-all-esp01-gpio-pins [2026/02/26 12:32] (current) – [Use case: Pins GPIO0 and GPIO2 as outputs] Ilias Iliopoulos
@@ Line 48: / Line 48: @@
 When ESP8266 boots, it checks the state of GPIO0, GPIO2 and GPIO15 to decide if it is going to run the program that is already stored in its flash memory, or it will enter a mode to load and flash a new program. To enter flash mode, GPIO0 must be LOW, GPIO2 must be HIGH and GPIO15 must be LOW. Pin GPIO15 is not exposed to the ESP-01 connector, so its not going to be of our concern.
-Pin GPIO0 needs to be in a HIGH state (that is, its voltage should be near Vcc) so that the stored program runs normally. If, for any reason,  the voltage at the pin is at a level that is considered by the processor as logic LOW, the processor will enter flash mode. Therefore, in order to use the pin for our purposes, we must make sure that the voltage is logic HIGH at start-up. Control circuits that are based on a "positive" logic, such the one presented below, result in pulling the pin voltage to LOW and therefore are inappropriate. Please note that the circuit below **DOES NOT WORK**.
+Pin GPIO0 needs to be in a HIGH state (that is, its voltage should be near Vcc) so that the stored program runs normally. If, for any reason,  the voltage at the pin is at a level that is considered by the processor as logic LOW, the processor will enter flash mode. Therefore, in order to use the pin for our purposes, we must make sure that the voltage is logic HIGH at start-up. Control circuits that are based on a "positive" logic, such the one presented below, result in pulling the pin voltage to LOW and therefore are inappropriate. Please note that the circuit below **MAY NOT WORK AS EXPECTED, IN ALL CIRCUMSTANCES**.
 {{ :esp8266:esp01_gpios_do_not_do.png|}}