ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 58

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

58
ATmega169/V
Consider the clock period starting shortly after the first falling edge of the system clock.
The latch is closed when the clock is low, and goes transparent when the clock is high,
as indicated by the shaded region of the “SYNC LATCH” signal. The signal value is
latched when the system clock goes low. It is clocked into the PINxn Register at the suc-
ceeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a
single signal transition on the pin will be delayed between ½ and 1½ system clock
period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as
indicated in Figure 25. The out instruction sets the “SYNC LATCH” signal at the positive
edge of the clock. In this case, the delay tpd through the synchronizer is 1 system clock
period.
Figure 25. Synchronization when Reading a Software Assigned Pin Value
INSTRUCTIONS
SYSTEM CLK
SYNC LATCH
PINxn
r16
r17
out PORTx, r16
0x00
nop
t
pd
0xFF
in r17, PINx
2514P–AVR–07/06
0xFF