Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
8 years, 4 months ago.
NUCLEO F091RC : Can I connect UART pins goto 5v?
Can I connect Serial 4 (PC_10 & PC_11) to RS485 breakout board which runs at 5v? Link to the breakout board : http://www.amazon.com/gp/product/B014QNI0BC/ref=pd_lpo_sbs_dp_ss_2/179-2993918-6718406?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=lpo-top-stripe-1&pf_rd_r=06JPAV938AX3A0X16Y1J&pf_rd_t=201&pf_rd_p=1944687542&pf_rd_i=B00AUE15BE
Thanks
2 Answers
8 years, 3 months ago.
Short answer: Yes.
Longer answer: Most but not all pins on the F091RC are 5 volt tolerant. Generally anything on an analog input isn't, most of the rest are. For the definitive list check the IO pins list on page 33 onward of the datasheet here. Anything listed with an IO structure of FT or FTf is ok with a 5V input, anything else is 3.3V max.
Not all UART pins are ok with 5V (e.g. PC2 & PC3 are 3.3V only) however the two you listed (PC10 & PC11) are both of type FT and should be fine with 5V inputs.
The driver counts anything over 2V as a high voltage so that's not an issue.
8 years, 3 months ago.
Generally it is possible to connect Nucleo outputs to RS485 inputs directly, but for RS485 outputs to Nucleo inputs you must use a small resistive divider, or a level (5V->3.3V) converter board.
Regards,
Why not consider a more suitable RS485 breakout board which operates from 3v3 to play it safe for use with any UART pin ?
For example,
http://www.amazon.com/Waveshare-SP3485-Transceiver-Converter-Communication/dp/B00UHFG8UO/ref=sr_1_1?s=electronics&ie=UTF8&qid=1452687999&sr=1-1&keywords=3.3v+rs485+board
Based on the Exar SP3485 transceiver.
Have you decided on the target baud rate for your application ?
Length of the cabling that will be used ?
Are you faced with heavy electrical noise ? Indoor or outdoor use for the RS485 nodes ?
How many RS485 nodes will be used in this project ?
You should consider ESD protection and/or surge protection and may even need to be galvanic isolated if faced with ground potential differences between nodes.
Our company is focused on communications and have been designing RS232,RS422,RS485 ports and adapters for 30 years to date.
posted by Sanjiv Bhatia 13 Jan 2016