To activate the usart on the CTS pin


How to activate brought by usart on the CTS and RTS pins?


Serial hardware flow control is not supported. For simple cases, you can drive a serial device’s CTS manually using any digital output to determine if the serial device should be sending the Photon data (LOW=send data, HIGH=stop). The problem is that there isn’t support for RTS to stop the flow of serial data out of the serial buffer to the serial device.


hi. thank you for help. is it same so the redbear letting?


Hardware flow control support is scheduled for 0.6.0:

Core: Serial1 (CTS - A0, RTS - A1)
Photon/Electron: Serial2 (CTS - A7, RTS - RGBR (which will require some tinkering to access))


thank you a lot for help.


Hi, did hardware flow control get added to electron? I’m looking to do some bidirectional communication on USART1 and didn’t seen any notes in the documentation to reflect this PR.



It was, however hardware flow control (CTS/RTS) is only available on Serial2 on the Photon and Electron.

Unfortunately Serial2 connected to the pins that operate the RGB LED, so you need to remove that (or its current-limiting resistors) in order to use hardware flow control on the Photon and Electron. CTS is A7 and RTS is RGBR.

This is how you access Serial2 on the Photon:


Thanks for the fast response! You’re right, the hw mods seem painful at scale, so I think handling in our software is the more efficient way to go. I appreciate the clean info though!