Rainbow Electronics ATmega128RFA1 - Manual (Page 407)

407
8266A-MCU Wireless-12/09
ATmega128RFA1
26 AC – Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and
negative pin AIN1. When the voltage on the positive pin AIN0 is higher than the voltage
on the negative pin AIN1, the Analog Comparator output, ACO, is set. The comparator’s
output can be set to trigger the Timer/Counter1 Input Capture function. In addition, the
comparator can trigger a separate interrupt, exclusive to the Analog Comparator. The
user can select Interrupt triggering on comparator output rise, fall or toggle. A block
diagram of the comparator and its surrounding logic is shown in
Figure 26-1 below .
The Power Reduction ADC bit PRADC in PRR0 (see "PRR0 – Power Reduction
Register0" on page 167 ) must be disabled by writing a logical zero to be able to use the
ADC input multiplexer.
Figure 26-1. Analog Comparator Block Diagram
Note:
1. See Table 26-1 below .
2. Refer to Figure 1-1 on page 2 and Table 14-9 on page 197 for Analog Comparator
pin placement.
26.1 Analog Comparator Multiplexed Input
It is possible to select any of the ADC7:0 pins as the negative input of the Analog
Comparator. The ADC multiplexer is used to select this input and consequently the
ADC must be switched off to utilize this feature. If the Analog Comparator Multiplexer
Enable bit (ACME in ADCSRB) is set and the ADC is switched off (ADEN in ADCSRA is
zero), MUX5 and MUX2:0 in ADMUX select the input pin to replace the negative input
to the Analog Comparator, as shown in
Table 26-1 below . If ACME is cleared or ADEN
is set, AIN1 is applied to the negative input to the Analog Comparator.
Table 26-1. Analog Comparator Multiplexed Input
ACME ADEN MUX5 MUX2:0 Analog Comparator Negative Input
0 x x xxx AIN1
1 1 x xxx AIN1
1 0 0 000 ADC0
1 0 0 001 ADC1
1 0 0 010 ADC2
1 0 0 011 ADC3
1 0 0 100 ADC4