53
ATmega8A [DATASHEET]
8159E–AVR–02/2013
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 pre-
viously 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.
13.2.3
Digital Input Enable and Sleep Modes
As shown in
Figure 13-2, the digital input signal can be clamped to ground at the input of the Schmitt-trigger. The
signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down mode, Power-save mode,
and Standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal
level close to V
CC/2.
SLEEP is overridden for port pins enabled as External Interrupt pins. If the External Interrupt Request is not
enabled, SLEEP is active also for these pins. SLEEP is also overridden by various other alternate functions as
If a logic high level (“one”) is present on an Asynchronous External Interrupt pin configured as “Interrupt on Rising
Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt is not enabled, the corresponding
External Interrupt Flag will be set when resuming from the above mentioned sleep modes, as the clamping in these
sleep modes produces the requested logic change.
:.
; 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
:.
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*/
_NOP();
/* Read port pins */
i = PINB;
:.