Rainbow Electronics ATmega64C1 - Manual (Page 257)

257
7647A–AVR–02/08
ATmega32/64/M1/C1
19.2.2 Voltage Reference for External Devices
An external resistor used in conjunction with the Current Source can be used as voltage refer-
ence for external devices. Using a resistor in serie with a lower tolerance than the Current
Source accuracy (
≤
2%) is recommended. Table 19-2 gives an example of voltage references
using standard values of resistors.
19.2.3 Threshold Reference for Internal Analog Comparator
An external resistor used in conjunction with the Current Source can be used as threshold refer-
ence for internal Analog Comparator (
See ”Analog Comparator” on page 258. ). This can be
connected to AIN0 (negative Analog Compare input pin) as well as AIN1 (positive Analog Com-
pare input pin). Using a resistor in serie with a lower tolerance than the Current Source accuracy
(
≤
2%) is recommended. Table 19-2 gives an example of threshold references using standard
values of resistors.
19.3 Control Register
19.3.1 ADC Control and Status Register B– ADCSRB
• Bit 6 – ISRCEN: Current Source Enable
Set this bit to source a 100µA current to the AREF pin.
Clear this bit to disconnect .
• Bit 5 – AREFEN: Analog Reference pin Enable
Set this bit to connect the internal AREF circuit to the AREF pin.
Clear this bit to disconnect the internal AREF circuit from the AREF pin.
Bit 7 6 5 4 3 2 1 0
ADHSM ISRCEN AREFEN - ADTS3 ADTS2 ADTS1 ADTS0 ADCSRB
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0