1. I/O Ports

2. I/O Ports Specs
Atmeg16 has 32 I/O ports (Ports A, B, C, D 8 lines each).
Each output buffer has symmetrical drive characteristics with both high sink and source capability.
The pin driver is strong enough to drive LED displays directly.
All port pins have individually selectable pull-up resistors.
All I/O pins have protection diodes to both VCC and Ground.

3. Port Registers
3 registers are dedicated to each port. So for example Port A has the following 3 bytes (control I/O registers) controlling its operation:
DATA Reg. 
Direction
Reg.
Pin Reg.
0->input pin
1->output pin

4. Ports’ Ssetting by CodeVision Wizard

5. I/O port and alternate functions

6. I/O port and alternate functions
Pullup is enabled lf:
Pullup-override w. value 1
OR write port a 1 and write direction 0 (input) together w. PUD (pullup disable in I/O Register SFIOR=0)

7. Most port pins have alternate functions in addition to being General Digital I/Os (see pin assignment).
PVOExn: Pxn PORT VALUE OVERRIDE ENABLE
PVOVxn: Pxn PORT VALUE OVERRIDE VALUE

8. ? Assignment: Design an Electronic Lock with arbitrary specs e.g.:
3 digits
Alarm after 3 trials
Master key