ATA5771 ATMEL Corporation, ATA5771 Datasheet - Page 107

• Manufacturer Part Number: ATA5771
• Manufacturer: ATMEL Corporation

10.2.2
10.2.3
10.2.4
8006G–AVR–01/08
Toggling the Pin
Switching Between Input and Output
Reading the Pin Value
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.
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}
= 0b10) as an intermediate step.
Table 10-1 on page 55
Table 10-1.
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in
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.
shows a timing diagram of the synchronization when reading an externally applied pin value.
The maximum and minimum propagation delays are denoted t
Figure 10-3. Synchronization when Reading an Externally Applied Pin value
DDxn
0
0
0
1
1
PORTxn
INSTRUCTIONS
0
1
1
0
1
Port Pin Configurations
SYSTEM CLK
SYNC LATCH
PINxn
(in MCUCR)
summarizes the control signals for the pin value.
r17
PUD
X
X
X
0
1
Figure 10-2 on page
XXX
Output
Output
Input
Input
Input
I/O
t
pd, max
Pull-up
0x00
Yes
No
No
No
No
XXX
54, the PINxn Register bit and the preced-
t
pd, min
Comment
Output Low (Sink)
Tri-state (Hi-Z)
Pxn will source current if ext. pulled low.
Tri-state (Hi-Z)
Output High (Source)
pd,max
in r17, PINx
ATtiny24/44/84
and t
pd,min
0xFF
respectively.
Figure 10-3
55