atmega323l ATMEL Corporation, atmega323l Datasheet - Page 135

• Manufacturer Part Number: atmega323l
• Description: Atmega323 8-bit Avr Microcontroller With 32k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Scanning Multiple
Channels
ADC Noise Canceling
Techniques
1457G–AVR–09/03
Since change of analog channel always is delayed until a conversion is finished, the
Free Running mode can be used to scan multiple channels without interrupting the con-
verter. Typically, the ADC Conversion Complete interrupt will be used to perform the
channel shift. However, the user should take the following fact into consideration:
The interrupt triggers once the result is ready to be read. In Free Running mode, the
next conversion will start immediately when the interrupt triggers. If ADMUX is changed
after the interrupt triggers, the next conversion has already started, and the old setting is
used.
Digital circuitry inside and outside the ATmega323 generates EMI which might affect the
accuracy of analog measurements. If conversion accuracy is critical, the noise level can
be reduced by applying the following techniques:
1. The analog part of the ATmega323 and all analog components in the application
2. Keep analog signal paths as short as possible. Make sure analog tracks run over
3. The AVCC pin on the ATmega323 should be connected to the digital V
4. Use the ADC noise canceler function to reduce induced noise from the CPU.
5. If some Port A pins are used as digital outputs, it is essential that these do not
Figure 65. ADC Power Connections
should have a separate analog ground plane on the PCB. This ground plane is
connected to the digital ground plane via a single point on the PCB.
the analog ground plane, and keep them well away from high-speed switching
digital tracks.
voltage via an LC network as shown in Figure 65.
switch while a conversion is in progress.
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PA4 (ADC4)
PA5 (ADC5)
PA6 (ADC6)
PA7 (ADC7)
AREF
AGND
AVCC
PC7
ATmega323(L)
CC
supply
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