Datasheet

ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
60
When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 10-4. 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 10-4. Synchronization when Reading a Software Assigned Pin Value
The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as
input with pull-ups assigned to port pins 6 and 7. The resulting pin values are read back again, but as previously discussed,
a nop instruction is included to be able to read back the value recently assigned to some of the pins.
Note: 1. For the assembly program, two temporary registers are used to minimize the time from pull-ups are set on pins
0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as
strong high drivers.
Assembly Code Example
(1)
...
; Define pull-ups and set outputs high
; Define directions for port pins
ldi r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)
ldi r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)
out PORTB,r16
out DDRB,r17
; Insert nop for synchronization
nop
; Read port pins
in r16,PINB
...
C Code Example
unsigned char i;
...
/* Define pull-ups and set outputs high */
/* Define directions for port pins */
PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);
DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);
/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
SYSTEM CLK
INSTRUCTIOS
SYNC LATCH
PINxn
r16
r17
out PORTx, r16 nop
0x00 0xFF
0xFF
in r17, PINx
t
pd