I am trying to implement Smart Card Reader( MFRC523 Reader) using Controller LPC2138 interface.

Link for datasheet: http://www.nxp.com/documents/data_sheet/MFRC523.pdf

I have interfaced MFRC523 smart card reader to LPC2138 using I2C protocol. For I2C interface, IC datasheet suggests NRSTPD pin to controller interface.

But due to shortage of I/O pin ( all I/Os used for other application ), I have hardwired NRSTPD pin to Logic High state.

As per datasheet,

NRSTPD ( Input ): ( reset and power-down input ) reset: enabled by a positive edge power-down: enabled when LOW; internal current sinks are switched off, the oscillator is inhibited and the input pins are disconnected from the outside world

So Can I hardwired NRSTPD pin to Logic High.

Please guide and thanks in advance.

  • \$\begingroup\$ I'm not sure what the question is. Are you asking if its okay to tie it to logic high? This shouldn't be an issue so long as you are okay with not being able to control the power state of the MFRC523 in your application code through the use of the reset pin \$\endgroup\$
    – Funkyguy
    Commented Apr 27, 2015 at 15:38
  • \$\begingroup\$ Ok.. My question is if I hardwire NRSTPD pin to High permanently ( hard wired instead assigning to I/O pin ), then functionality wise is there any issue. Card Reader will able to read card or not? \$\endgroup\$ Commented Apr 27, 2015 at 15:53
  • \$\begingroup\$ You should be fine. The reset functionality looks like it is enabled by the positive edge of a pulse, the power down is active when it is low so if you tie it to high, you should be fine \$\endgroup\$
    – Funkyguy
    Commented Apr 27, 2015 at 15:56

1 Answer 1


It looks like the reset functionality of that pin is enabled by the positive edge of a pulse and the power down is enabled by pulling it LOW, so if you have the pin tied to HIGH, there won't be positive edge of a pulse to reset the chip, during normal operation, and power down won't happen cause it isn't low.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.