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251
2593O–AVR–02/12
ATmega644
21.9.3
ADCL and ADCH – The ADC Data Register
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 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.
ADC9:0: ADC Conversion Result
21.9.4
ADCSRB – ADC Control and Status Register B
Bit 7, 5:3 – Res: Reserved Bits
These bits are reserved for future use in the ATmega644. For ensuring compability with future
devices, these bits must be written zero when ADCSRB is written.
Bit 2:0 – ADTS2:0: 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
Bit
15
14131211
10
9
8
––––––
ADC9
ADC8
ADCH
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0
ADCL
765432
10
Read/Write
RRRR
Initial Value
000000
00
000000
00
Bit
15
14131211
10
9
8
ADC9
ADC8
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADCH
ADC1
ADC0
–––––
–
ADCL
7654321
0
Read/Write
RRRR
Initial Value
0000000
0
0000000
0
Bit
7
65
4
3
21
0
–
ACME
–
ADTS2
ADTS1
ADTS0
ADCSRB
Read/Write
R
R/W
R
R/W
Initial Value
0