I was looking to create a LPC1343 development board, but I noticed something odd. If you look at the pinout for this MCU you can see double functions for some pins. This is common, so you can program a pin to use for a particular function. But here is the weird thing. Pin 3 on the LPC1343 says: "RESET/PIO0_0". Now I'm confused. How can a reset pin also be a I/O pin? I can't find anything about it in the datasheet.

LPC1343 pinout LPC1343 pin description

Any help would be appreciated. Thanks in advance.

  • \$\begingroup\$ Are you sure there isn't another reset button? \$\endgroup\$ – rrz0 Jan 6 '18 at 15:07

Looking in the user manual if actually found the pin function register. You can, just like the other pins, switch the function via this register. Which I still find odd, because you wouldn't be able te reset the MCU anymore using an external pin. But apparently they did design it this way.

PIO0_0/RESET pin function register

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    \$\begingroup\$ Some designs don't need the reset and would rather have the pins. You may find it more confusing that some processors (like yours) can switch the programming pins to gpio as well. This is where bootloader code can switch them back to reset/programming, you just need a way to enter the bootloader. \$\endgroup\$ – Ron Beyer Jan 6 '18 at 14:26
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    \$\begingroup\$ I dont know the chip in the question but the same thing can be found on an ATtiny45: Once you set the pin as a GPIO, you'll never be able to re-program the chip due to the lack of a reset pin. The only way is applying a special process with a special hardware to reset the chip to factory defaults. So care should be taken on the LPC1343. \$\endgroup\$ – Rohat Kılıç Jan 6 '18 at 14:31

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