Datasheet

142
2586N–AVR–04/11
ATtiny25/45/85
are supported and the voltage on the positive input must always be larger than the voltage on
the negative input. Otherwise the result is saturated to the voltage reference. In the bipolar mode
two-sided conversions are supported and the result is represented in the two’s complement
form. In the unipolar mode the resolution is 10 bits and the bipolar mode the resolution is 9 bits +
1 sign bit.
• Bit 5 – IPR: Input Polarity Reversal
The Input Polarity mode allows software selectable differential input pairs and full 10 bit ADC
resolution, in the unipolar input mode, assuming a pre-determined input polarity. If the input
polarity is not known it is actually possible to determine the polarity first by using the bipolar input
mode (with 9 bit resolution + 1 sign bit ADC measurement). And once determined, set or clear
the polarity reversal bit, as needed, for a succeeding 10 bit unipolar measurement.
• Bits 4:3 – Res: Reserved Bits
These bits are reserved bits in the ATtiny25/45/85 and will always read as zero.
• Bits 2:0 – ADTS[2:0]: ADC Auto Trigger Source
If ADATE in ADCSRA is written to one, the value of these bits selects which source will trigger
an ADC conversion. If ADATE is cleared, the ADTS[2:0] settings will have no effect. A conver-
sion will be triggered by the rising edge of the selected Interrupt Flag. Note that switching from a
trigger source that is cleared to a trigger source that is set, will generate a positive edge on the
trigger signal. If ADEN in ADCSRA is set, this will start a conversion. Switching to Free Running
mode (ADTS[2:0]=0) will not cause a trigger event, even if the ADC Interrupt Flag is set
.
17.13.5 DIDR0 – Digital Input Disable Register 0
• Bits 5:2 – ADC3D:ADC0D: ADC[3:0] Digital Input Disable
When this bit is written logic one, the digital input buffer on the corresponding ADC pin is dis-
abled. The corresponding PIN register bit will always read as zero when this bit is set. When an
analog signal is applied to the ADC[3:0] pin and the digital input from this pin is not needed, this
bit should be written logic one to reduce power consumption in the digital input buffer.
Table 17-6. ADC Auto Trigger Source Selections
ADTS2 ADTS1 ADTS0 Trigger Source
0 0 0 Free Running mode
0 0 1 Analog Comparator
0 1 0 External Interrupt Request 0
0 1 1 Timer/Counter0 Compare Match A
1 0 0 Timer/Counter0 Overflow
1 0 1 Timer/Counter0 Compare Match B
1 1 0 Pin Change Interrupt Request
Bit 76543210
0x14
– – ADC0D ADC2D ADC3D ADC1D AIN1D AIN0D DIDR0
Read/Write R R R/W R/W R/W R/W R/W R/W
Initial Value00000000