ATMEGA644PV-20AU Atmel, ATMEGA644PV-20AU Datasheet - Page 247
![IC MCU AVR 64K FLASH 44-TQFP](/photos/6/70/67042/313-44-tqfp_sml.jpg)
ATMEGA644PV-20AU
Manufacturer Part Number
ATMEGA644PV-20AU
Description
IC MCU AVR 64K FLASH 44-TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA644PV-20AU
Core Processor
AVR
Core Size
8-Bit
Speed
20MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
32
Program Memory Size
64KB (32K x 16)
Program Memory Type
FLASH
Eeprom Size
2K x 8
Ram Size
4K x 8
Voltage - Supply (vcc/vdd)
1.8 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
44-TQFP, 44-VQFP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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20.6.1
20.6.2
8011O–AVR–07/10
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.
Special care should be taken when changing differential channels. Once a differential channel
has been selected, the gain stage may take as much as 125 µs to stabilize to the new value.
Thus conversions should not be started within the first 125 µs after selecting a new differential
channel. Alternatively, conversion results obtained within this period should be discarded.
The same settling time should be observed for the first differential conversion after changing
ADC reference (by changing the REFS1:0 bits in ADMUX).
When changing channel selections, the user should observe the following guidelines to ensure
that the correct channel is selected:
In Single Conversion mode, always select the channel before starting the conversion. The chan-
nel 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.
In Free Running mode, always select the channel before starting the first conversion. The chan-
nel 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.
When switching to a differential gain channel, the first conversion result may have a poor accu-
racy due to the required settling time for the automatic offset cancellation circuitry. The user
should preferably disregard the first conversion result.
The reference voltage for the ADC (V
ended channels that exceed V
either AVCC, internal 2.56V reference, or external AREF pin.
AVCC is connected to the ADC through a passive switch. The internal 2.56V reference is gener-
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.
1.
2.
3.
When ADATE or ADEN is cleared.
During conversion, minimum one ADC clock cycle after the trigger event.
After a conversion, before the Interrupt Flag used as trigger source is cleared.
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
ATmega164P/324P/644P
REF
can be selected as
REF
is a high
REF
247
can
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