shredder929
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I've got an odd problem here. I have this board with an MSP430F5435, and pins 39 and 40 are being used for UART communication, going to a port used for configuration through a PC app. The port is 4 pins, Rx, Tx, GND, Vcc. Pin 40 is the Rx line, pulled up to Vcc by a 100k resistor. Pin 39 is Tx and goes straight to the config port, no external pulllup/pulldown.
Normally when the device is off, pin 39 is just open, and then when powered on, the MSP internally pulls it to GND and then goes up and down as needed to transmit. But I have a couple devices here that can't communicate over UART because pin 39 is hard shorted to GND internally to the MSP. Even when the board is powered off, the Tx line is shorted to GND. I pulled the pad off the board, even pulled the pin off the body, and found the body contact for the Tx line is shorted to GND, so it's definitely an issue in the MSP itself. Because it's shorted, the MSP can never assert high and cannot transmit. We have found that they can receive though. If I send a reboot command from my PC app, it reboots, the MSP is running its code fine otherwise, we just don't get any feedback.
These units were tested and working fine when they left, some got this problem after being in the field for a year, but I have one that got this problem when it got to the customer. The cable is just a USB serial cable, FTDI driver, nothing special. Plugging it in backwards or offset and stuff doesn't seem to break anything. We don't think its ESD either.
Have any of you seen this issue before, where an MSP pin is inexplicably shorted to GND internally even when off?
Normally when the device is off, pin 39 is just open, and then when powered on, the MSP internally pulls it to GND and then goes up and down as needed to transmit. But I have a couple devices here that can't communicate over UART because pin 39 is hard shorted to GND internally to the MSP. Even when the board is powered off, the Tx line is shorted to GND. I pulled the pad off the board, even pulled the pin off the body, and found the body contact for the Tx line is shorted to GND, so it's definitely an issue in the MSP itself. Because it's shorted, the MSP can never assert high and cannot transmit. We have found that they can receive though. If I send a reboot command from my PC app, it reboots, the MSP is running its code fine otherwise, we just don't get any feedback.
These units were tested and working fine when they left, some got this problem after being in the field for a year, but I have one that got this problem when it got to the customer. The cable is just a USB serial cable, FTDI driver, nothing special. Plugging it in backwards or offset and stuff doesn't seem to break anything. We don't think its ESD either.
Have any of you seen this issue before, where an MSP pin is inexplicably shorted to GND internally even when off?