ATTINY15 ATMEL [ATMEL Corporation], ATTINY15 Datasheet - Page 49

• Manufacturer Part Number: ATTINY15
• Manufacturer: ATMEL [ATMEL Corporation]

Scanning Multiple Channels
ADC Noise-canceling
Techniques
1187D–12/01
When an ADC conversion is complete, the result is found in these two registers. When
ADCL is read, the ADC Data Register is not updated until ADCH is read. 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 affects 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
These bits represent the result from the conversion. For the differential channel, this is
the value after gain adjustment, as indicated in Table 20 on page 47. For single-ended
conversion, or if ADLAR or SIGN is zero, $000 represents ground and $3FF represents
the selected reference voltage minus one LSB.
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:
Digital circuitry inside and outside the ATtiny15L 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 ATtiny15L and all analog components in the application
2. Keep analog signal paths as short as possible. Make sure analog tracks run over
3. Use the ADC noise canceler function to reduce induced noise from the CPU.
4. If some Port B pins are used as digital outputs, it is essential that these do not
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.
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.
switch while a conversion is in progress.
ATtiny15L
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