SN65HVD72: use the signal between A and B of 485 to drive a led。

Hi,

I don't think SN74LVC8T245 would put much load on RS485 output. But to make it work, you need to choose the resistors (R248, R247, R253) to make the voltage level work with B1 and B2's Vih and Vil. From my understanding, the purpose of the circuit is having a visual indicator of valid RS485 signaling on bus . If so, since the RX of transceiver is on, you could use R (pin 1) to drive the led. Please let me know if you have more questions.

Regards,
Hao

because  the Tx or rx of  U36 is not connected  to  the terminal，but  the  a and  b  signal is  connected  to  the terminal 。 now  i want to make a test board  ，finally，i will apply this scheme。but i have  a question，as you  see now  i convert the a and  b signal to tx signal ，so is it  necessary  to still  use  245  chip  to driver  the led？if i do not use 245 chip，will there be a problem？