Datasheet

8018P–AVR–08/10

ATmega169P

13.2.2 Toggling the Pin

Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.

Note that the SBI instruction can be used to toggle one single bit in a port.

13.2.3 Switching Between Input and Output

When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}

= 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output

low ({DDxn, PORTxn} = 0b10) must occur. Normally, the pull-up enabled state is fully accept-

able, as a high-impedant environment will not notice the difference between a strong high driver

and a pull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all

pull-ups in all ports.

Switching between input with pull-up and output low generates the same problem. The user

must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}

= 0b11) as an intermediate step.

Table 13-1 summarizes the control signals for the pin value.

13.2.4 Reading the Pin Value

Independent of the setting of Data Direction bit DDxn, the port pin can be read through the

PINxn Register bit. As shown in Figure 13-2 on page 66, the PINxn Register bit and the preced-

ing latch constitute a synchronizer. This is needed to avoid metastability if the physical pin

changes value near the edge of the internal clock, but it also introduces a delay. Figure 13-3 on

page 68 shows a timing diagram of the synchronization when reading an externally applied pin

value. The maximum and minimum propagation delays are denoted t

pd,max

and t

pd,min

respectively.

Table 13-1. Port Pin Configurations

DDxn PORTxn

PUD

(in MCUCR) I/O Pull-up Comment

0 0 X Input No Tri-state (Hi-Z)

0 1 0 Input Yes Pxn will source current if ext. pulled low.

0 1 1 Input No Tri-state (Hi-Z)

1 0 X Output No Output Low (Sink)

1 1 X Output No Output High (Source)