62
ATmega16M1/32M1/64M1 [DATASHEET]
8209E–AVR–11/2012
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 inter-
mediate 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 acceptable, 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
needed to avoid metastability if the physical pin changes value near the edge of the internal clock, but it also intro-
duces a delay.
Figure 13-3 on page 62 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 tpd,min respectively.
Figure 13-3. Synchronization when reading an externally applied pin value.
Table 13-1.
Port pin configurations.
DDxn
PORTxn
PUD
(in MCUCR)
I/O
Pull-up
Comment
0
X
Input
No
Default configuration after reset
tri-state (Hi-Z)
0
1
0
Input
Yes
Pxn will source current if ext. pulled low
0
1
Input
No
Tri-state (Hi-Z)
1
0
X
Output
No
Output low (sink)
1
X
Output
No
Output high (source)
XXX
in r17, PINx
0x00
0xFF
INSTRUCTIONS
SYNC LATCH
PINxn
r17
XXX
SYSTEM CLK
t
pd, max
t pd, min