AT90PWM216-16SE ATMEL [ATMEL Corporation], AT90PWM216-16SE Datasheet - Page 242

• Manufacturer Part Number: AT90PWM216-16SE
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable flash
• Manufacturer: ATMEL [ATMEL Corporation]

21.5.1
21.5.2
242
AT90PWM216/316
ADC Input Channels
ADC Voltage Reference
If Auto Triggering is used, the exact time of the triggering event can be indeterministic. Special
care must be taken when updating the ADMUX Register, in order to control which conversion
will be affected by the new settings.
If both ADATE and ADEN is written to one, an interrupt event can occur at any time. If the
ADMUX Register is changed in this period, the user cannot tell if the next conversion is based
on the old or the new settings. ADMUX can be safely updated in the following ways:
When updating ADMUX in one of these conditions, the new settings will affect the next ADC
conversion.
In order to start a conversion on an amplified channel, there is a dedicated ADASCR bit in ADC-
SRB register which wait for the next amplifier trigger event before really starting the conversion
by an hardware setting of the ADSC bit in ADCSRA register.
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
The reference voltage for the ADC (V
ended channels that exceed V
either AV
AV
ated from the internal bandgap reference (V
external AREF pin is directly connected to the ADC, and the reference voltage can be made
more immune to noise by connecting a capacitor between the AREF pin and ground. V
also be measured at the AREF pin with a high impedant voltmeter. Note that V
impedant source, and only a capacitive load should be connected in a system.
If the user has a fixed voltage source connected to the AREF pin, the user may not use the other
reference voltage options in the application, as they will be shorted to the external voltage. If no
external voltage is applied to the AREF pin, the user may switch between AV
• In Single Conversion mode, always select the channel before starting the conversion. The
• In Free Running mode, always select the channel before starting the first conversion. The
• In Free Running mode, because the amplifier clear the ADSC bit at the end of an amplified
CC
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the conversion to complete before changing the channel
selection.
channel selection may be changed one ADC clock cycle after writing one to ADSC. However,
the simplest method is to wait for the first conversion to complete, and then change the
channel selection. Since the next conversion has already started automatically, the next
result will reflect the previous channel selection. Subsequent conversions will reflect the new
channel selection.
conversion, it is not possible to use the free running mode, unless ADSC bit is set again by
soft at the end of each conversion.
a. When ADATE or ADEN is cleared.
b. During conversion, minimum one ADC clock cycle after the trigger event.
c. After a conversion, before the interrupt flag used as trigger source is cleared.
is connected to the ADC through a passive switch. The internal 2.56V reference is gener-
CC
, internal 2.56V reference, or external AREF pin.
REF
will result in codes close to 0x3FF. V
REF
) indicates the conversion range for the ADC. Single
BG
) through an internal amplifier. In either case, the
REF
can be selected as
CC
7710D–AVR–08/09
and 2.56V as
REF
is a high
REF
can