MSP430F247: Strange behaviour of microcontroller - UART reception only when touched the RX pin by finger

kiran patil20

Part Number: MSP430F247

Hello,

I am working on RS-485 communication on MSP430f247. I have interfaced IL3085 RS485 Transceiver to MSP430F247. Using 9600 baud rate for communication.

I am monitoring the data traffic on MODSCAN32 using USB to RS-485 converter.

On MODSCAN software I am getting valid responses to queries but only when I am touching RX pin when removed no response received.

Also, I have tried on 19200 baud rate but its not working in any case even touched to RX pin.

I have checked all the grounding, voltage levels everything found ok.

Can anyone have suggestions to this strange problem, please?

I have attached schematic for ready reference.

over 8 years ago

0 Clemens Ladisch over 8 years ago

Guru 318760 points

What are you touching? The signal labelled "RXD" in the schematic, or the MSP's RXD pin?

Do you see the correct signal levels with an oscilloscope?

0 kiran patil20 over 8 years ago in reply to Clemens Ladisch

Prodigy 30 points

Hello Clemens,

I was touching MSP RXD pin (P3.7) to make the communication successful.

Thanks for the immediate reply and support.

My problem resolved now working as intended.

The reason is - RX signal track is quite long and through two vias on the PCB to reach to RS485 transceiver. So I disconnect the track and made the direct connection using wire and the problem solved.

0 kiran patil20 over 8 years ago in reply to kiran patil20

Prodigy 30 points

Hi Clemens,

In continuation with above problem I have modified the PCB layout and kept shortest track between RS485 transceiver and MSP430F247 without vias, still I have facing the same problem, when touching RX pin only then UART receive interrupt occur.

This is seems to be very strange. I am using 8MHz clock frequency for UART. Is this is because of high frequency?

Please suggest any guidelines to tackle this behavior.

0 Clemens Ladisch over 8 years ago in reply to kiran patil20

Guru 318760 points

Do you see the correct signal levels with an oscilloscope?

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MSP430F247: Strange behaviour of microcontroller - UART reception only when touched the RX pin by finger