LPc4357 uart problem

[Ashrumochan]

Hello Guys,
I am using two LPC4357 Microcontroller to establish uart protocol.
One card uart2 and other uart3.
I did all configuration and hardware connections and able to transmit and receive properly in both the cards. But all of a sudden Card 1 transmiiting but unable to receive.
I checked everythinh as I have not done any changes in software as well as hardware.
I could see the voltage at TX pin is 3.4v but at RX pin is 2.4v which feels like controller rx pin is driving low.

In other board both tx and rx pin have same voltage.
What might be the issue ?
I am able to load and debug anyway the other uart pins are working I checked except uart 2-> rx pin is behaving awkward.

Can anybody suggest di need to replace the controller or anyway it can be get worked or how it happened like this?

Waiting for your quick response.

[xiangjun_rong]

Hi, Ashrumochan,

As you said that the Uart_Rx pin logic voltage is 2.4v, I think it is abnormal, if you unplug  the UART card, and test the UART card TX pin logic(the pin is not connected to the RX pin of LPC4357) , what is the logic voltage? If the UART card Tx logic voltage is 3.3V, after the pin is connected to RX pin of LPC4357, the logic voltage becomes to 2.4V, I suppose the UART of LPC4357 is damaged.

Hope it can help you

BR

XiangJun Rong

[Ashrumochan]

Hello XiangJun ,
Thank you for your kind reply.
As you told UART block is damaged.
So I was wondering to know how even this possible that one pin getting damaged while all other ports are working as expected.
Is it the noise or power supply issue which can cause this?
Because I was trying to add extra pullup across the RX pin though still its not working.
Another thing ,I   observed that , from RX to my ground pin the resistance should be around 5megaohm while it was working fine.
But after it got damaged its resistance is decreased to around 450ohm.
So If I   tried to add across the RX pin some resistor to bring it to same 5megaohm but still it didn't work for me.
Can you please clarify if anything or replacement is the only solution for above issue?

Thank & Regards,
Ashrumochan

[xiangjun_rong]

Hi,

Frankly speaking, I do not know why the Uart_RX pin is damaged, maybe the cause is noise, static charge...

I suggest you add a ESD device on the Uart_Rx pin to protect the RX internal circuit.

Currently, I suggest you replace the chip with a new one.

Hope it can help you

BR

XiangJun Rong

[Ashrumochan · Accepted solution]

Thanks for your time and value added feedback.

Regards,

Ashrumochan