Datasheet

 2018 Microchip Technology Inc. Data Sheet Complete DS40002060A-page 52
ATtiny4/5/9/10
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an out-
put pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is
written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).
The pull-up resistor is activated, if the PUExn is written logic one. To switch the pull-up resistor off, PUExn has to be written
logic zero.
Table 11-1 summarizes the control signals for the pin value.
Port pins are tri-stated when a reset condition becomes active, even when no clocks are running.
11.2.2 Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn. Note that the SBI instruc-
tion can be used to toggle one single bit in a port.
11.2.3 Break-Before-Make Switching
In Break-Before-Make mode, switching the DDRxn bit from input to output introduces an immediate tri-state period lasting
one system clock cycle, as indicated in Figure 11-3. For example, if the system clock is 4 MHz and the DDRxn is written to
make an output, an immediate tri-state period of 250 ns is introduced before the value of PORTxn is seen on the port pin.
To avoid glitches it is recommended that the maximum DDRxn toggle frequency is two system clock cycles. The Break-
Before-Make mode applies to the entire port and it is activated by the BBMx bit. For more details, see “PORTCR – Port
Control Register” on page 60.
When switching the DDRxn bit from output to input no immediate tri-state period is introduced.
Table 11-1. Port Pin Configurations
DDxn PORTxn PUExn I/O Pull-up Comment
0X
0
Input No Tri-state (hi-Z)
0X
1
Input Yes Sources current if pulled low externally
10
0
Output No Output low (sink)
10
1
Output Yes
NOT RECOMMENDED.
Output low (sink) and internal pull-up active.
Sources current through the internal pull-up
resistor and consumes power constantly
11
0
Output No Output high (source)
11
1
Output Yes Output high (source) and internal pull-up active