Datasheet

289
7682C–AUTO–04/08
AT90CAN32/64/128
• Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the XTAL frequency and the input clock to the
ADC.
21.8.3 The ADC Data Register – ADCL and ADCH
ADLAR = 0
ADLAR = 1
When an ADC conversion is complete, the result is found in these two registers. If differential
channels are used, the result is presented in two’s complement form.
When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if
the result is left adjusted and no more than 8-bit precision (7 bit + sign bit for differential input
channels) is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then
ADCH.
The ADLAR bit in ADMUX, and the MUXn bits in ADMUX affect the way the result is read from
the registers. If ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result
is right adjusted.
Table 21-5. ADC Prescaler Selections
ADPS2 ADPS1 ADPS0 Division Factor
0 0 0 2
0 0 1 2
0 1 0 4
0 1 1 8
1 0 0 16
1 0 1 32
1 1 0 64
1 1 1 128
Bit 15 14 13 12 11 10 9 8
– – – – – – ADC9 ADC8 ADCH
ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADC1 ADC0 ADCL
Bit 7 6 5 4 3 2 1 0
Read/Write R R R R R R R R
R R R R R R R R
Initial Value 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
Bit 15 14 13 12 11 10 9 8
ADC9 ADC8 ADC7 ADC6 ADC5 ADC4 ADC3 ADC2 ADCH
ADC1 ADC0 – – – – – – ADCL
Bit 7 6 5 4 3 2 1 0
Read/Write R R R R R R R R
R R R R R R R R
Initial Value 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0