About Unused pin handling (S12P family)

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About Unused pin handling (S12P family)

545件の閲覧回数
Lucidfall
Contributor I

Hello everyone.  I'm using MC9S12P64 Micom.

 

 If there are unused pins in application, What is best way to handle it ?

 

For example,

 

 Configure data direction register output and set data register '0' (floating, do not need to connect)

 

 Configure DDR input and tie to gnd or Vdd with Internal Pull-up register

 

If there are documents I can refer to, it is welcome.

(I found AN2727 about HCS12 D-family but I can not find about MC9S12P-family)

 

Thanks for your reply.

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kef
Specialist I

You need to prevent floating of unused pins. This may be done setting pin direction to output, enabling internal pull up or connecting to Vdd or Vss. All measures are almost equally good. 

Connecting to supply rails is good for input only pins, but questionable for bidirectional pins, because accidentally (think about possible software defect) pin direction may be flipped to output. So bidirectional I/O pin should be connected to supply rail via current limiting resistor, which would increase components count.

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