RS232 Connector Pin Assignment
RS232 Cable Information
DB 9 and DB 25 Connection

The original pin layout for RS232 was developed for a 25 pins D sub connector.  In this pin-out provisions were made for a secondary communication channel. In practice, only one communication channel with accompanying handshaking is present. For that reason the smaller 9 pin version is more commonly used today.
The diagrams show the signals common to both connector types in black. The signals only present on the larger connector are shown in red.
Note: The protective ground is assigned to a pin at the large connector, in DB9 version protective ground connector to encloser.
For the DEC modified modular jack. Although is differential (the receive and transmit have their own floating ground level) still possible to connect RS232 compatible devices with this interface.

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This article is a guide for the ESP8266 GPIOs: pinout diagrams, their functions and how to use them.


The ESP8266 12-E chip comes with 17 GPIO pins. Not all GPIOs are exposed in all ESP8266 development boards, some GPIOs are not recommended to use, and others have very specific functions.

With this guide, you’ll learn how to properly use the ESP8266 GPIOs and avoid hours of frustration by using the most suitable pins for your projects.

We also have a guide for the ESP32 GPIOs: ESP32 Pinout Reference: Which GPIO pins should you use?

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