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ATtiny22/22L
General Digital I/O
All pins in port B have equal functionality when used as digital I/O pins.
PBn, General I/O pin: The DDBn bit in the DDRB register selects the direction of this pin, if DDBn is set (one), PBn is con-
figured as an output pin. If DDBn is cleared (zero), PBn is configured as an input pin. If PORTBn is set (one) when the pin
configured as an input pin, the MOS pull up resistor is activated. To switch the pull up resistor off, the PORTBn has to be
cleared (zero) or the pin has to be configured as an output pin. The port pins are tri-stated when a reset condition becomes
active, even if the clock is not running.
Alternate Functions of Port B
The alternate pin functions of Port B are:
CLOCK - Port B, Bit 3
Clock input: When the RCEN fuse is programmed and the device runs from the internal RC oscillator, this pin is a general
I/O pin. When the RCEN Fuse is unprogrammed, an external clock source must be connected to CLOCK.
SCK/T0 - Port B, Bit 2
In serial programming mode, this bit serves as the serial clock input, SCK.
During normal operation, this pin can serve as the external counter clock input. See the timer/counter description for further
details. If external timer/counter clocking is selected, activity on this pin will clock the counter even if it is configured as an
output.
MISO - Port B, Bit 1
In serial programming mode, this bit serves as the serial data output, MISO.
During normal operation, this pin can serve as the external interrupt0 input. See the interrupt description for details on how
to enable this interrupt. Note that activity on this pin will trigger the interrupt even if the pin is configured as an output.
MOSI - Port B, Bit 0
In serial programming mode, this pin serves as the serial data input, MOSI.
Table 11. DDBn Effects on Port B Pins
DDBn
PORTBn
I/O
Pull up
Comment
0
0
Input
No
Tri-state (Hi-Z)
0
1
Input
Yes
PBn will source current if ext. pulled low.
1
0
Output
No
Push-Pull Zero Output
1
1
Output
No
Push-Pull One Output
