Current drain rises when digital input floats between '0' and '1' levels. To eliminate it do one of the following on all your unused digital inputs:
1) turn input to output using data direction registers
2) enable pull device, both pull-up and pull-down are OK.
3) pull inputs externally to I/O supply rails, usually vss or vdd
Since lower pin count packages may have non bonded out pin pads, you should not forget to turn them into outputs as well.
Edward
Current drain rises when digital input floats between '0' and '1' levels. To eliminate it do one of the following on all your unused digital inputs:
1) turn input to output using data direction registers
2) enable pull device, both pull-up and pull-down are OK.
3) pull inputs externally to I/O supply rails, usually vss or vdd
Since lower pin count packages may have non bonded out pin pads, you should not forget to turn them into outputs as well.
Edward