ATMEGA16 Datasheet, PDF (50/315 Pages) ATMEL Corporation – 8-bit AVR Microcontroller with 16K Bytes In-System Programmable Flash

succeeding positive clock edge. As indicated by the two arrows t_pd,max and t_pd,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 t_pd through the synchronizer is one system
clock period.
Figure 25. Synchronization when Reading a Software Assigned Pin Value
SYSTEM CLK
r16
INSTRUCTIONS
SYNC LATCH
PINxn
r17
out PORTx, r16
0xFF
nop
in r17, PINx
0x00
t_pd
0xFF
50 ATmega16(L)
2466E–AVR–10/02