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MSP430F5342: Booting Failure

Nachiketh Karanth

Intellectual 840 points

Part Number: MSP430F5342

Hi Team,

We are using MSP430F5342IRGZR in our custom board. MSP is used to power ON the board.

When UART of MSP is not connected through cable, MSP boots and board powers ON. But when UART of MSP is connected, MSP itself does not boot.

Please provide your inputs in solving the issue.

Thanks

0 David Schultz 6 months ago

Guru 25955 points

Most likely from failure to understand basic electronics.

If that UART connection is powered, it supplies power to the MSP430. Causing the voltage at a pin to violate the absolute voltage limit. Which is in terms of Vcc plus. If no power is supplied to the MSP430 on Vcc...

This violation forward biases the internal MSP430 protection diode pulling up Vcc. For a low power device like the MSP430 it doesn't take much to keep it powered. Or at least cause trouble.

0 Nachiketh Karanth 6 months ago

Intellectual 840 points

Thanks for the input.
Forward-biasing through UART isn’t exactly an exotic concept — we’re aware of protection-diode back-power effects. The point of the post was to understand why it happens specifically on this board and whether there are MSP430-specific caveats we might be missing.

If you have any device-level insights beyond ‘basic electronics,’ that would actually help move the debug forward.

Best Regards

0 David Schultz 6 months ago in reply to Nachiketh Karanth

Guru 25955 points

Nachiketh Karanth said:
specifically on this board

What board?

0 Nachiketh Karanth 6 months ago in reply to David Schultz

Intellectual 840 points

In our custom board

0 Keith Barkley 6 months ago in reply to Nachiketh Karanth

Guru 43175 points

What are you connecting the UART to? I certainly hope it is not an RS-232 port.

Observe the device Vcc in both states.

Try connecting the UART via an isolator.

0 Nachiketh Karanth 6 months ago in reply to Keith Barkley

Intellectual 840 points

We are using TTL-232R-3V3 cable to connect it to USB port in PC.

Measure VCC in both states, Do you mean Board ON and OFF state?

Is there any specific IC or device for isolation? How are you suggesting to isolate the UART signals?

0 Keith Barkley 6 months ago in reply to Nachiketh Karanth

Guru 43175 points

Two States:

Connected and not-connected.

Can you link to your cable?

https://www.digikey.com/en/products/detail/advantech-corporation/BB-232SPHI4/4170059

You can try to boot by connecting *only* the ground of the cable, none of the signal lines.

0 Nachiketh Karanth 6 months ago in reply to Keith Barkley

Intellectual 840 points

Cable used TTL-232R-3V3, Link is below :

https://www.digikey.in/en/products/detail/ftdi-future-technology-devices-international-ltd/TTL-232R-3V3/1836393

When connecting only the ground cable, MSP is booting.

0 Keith Barkley 6 months ago in reply to Nachiketh Karanth

Guru 43175 points

Well there you go, now you know where the problem is. How exactly are you making the other connections?

0 Nachiketh Karanth 6 months ago in reply to Keith Barkley

Intellectual 840 points

Since the UART RX pin of cable will backdrive voltage to MSP, should we plug the UART TX,RX and GND pins of cable after the MSP boots?

0 Nachiketh Karanth 6 months ago in reply to Nachiketh Karanth

Intellectual 840 points

Hi Keith,

Since the UART RX pin of cable will backdrive voltage to MSP, should we plug the UART TX,RX and GND pins of cable after the MSP boots?

0 Keith Barkley 5 months ago in reply to Nachiketh Karanth

Guru 43175 points

If Vcc is present it is not necessary. Otherwise, hold the unit in reset until everything is ready.

0 Nachiketh Karanth 5 months ago in reply to Keith Barkley

Intellectual 840 points

By VCC, do you mean the power back-driving through cable or the power given to MSP on-board?

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