ATmega168 Automotive Atmel Corporation, ATmega168 Automotive Datasheet - Page 139

• Manufacturer Part Number: ATmega168 Automotive
• Manufacturer: Atmel Corporation

Specifications of ATmega168 Automotive

• Flash (kbytes): 16 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 24
• Usb Speed: No
• Usb Interface: No
• Spi: 2
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 1
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 150
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

18.4
7701E–AVR–02/11
Starting a Conversion
If differential channels are selected, the differential gain stage amplifies the voltage difference
between the selected input pair by the selected gain factor, 1x or 20x, according to the setting
of the MUX0 bit in the ADMUX register. This amplified value then becomes the analog input to
the ADC. If single-ended channels are used, the gain amplifier is bypassed altogether.
The offset of the differential channels can be measure by selecting the same input for both
negative and positive input. Offset calibration can be done for ADC0, ADC3 and ADC7. When
ADC0, ADC3, or ADC7 is selected as both the positive and negative input to the differential
gain amplifier, the remaining offset in the gain stage and conversion circuitry can be measured
directly as the result of the conversion. This figure can be subtracted from subsequent conver-
sions with the same gain setting to reduce offset error to below 1 LSB.
The on-chip temperature sensor is selected by writing "100010" to the MUX5..0 bits in the
ADMUX register.
The ADC is enabled by setting the ADC enable bit (ADEN) in ADCSRA. Voltage reference and
input channel selections will not go into effect until ADEN is set. The ADC does not consume
power when ADEN is cleared, so it is recommended to switch off the ADC before entering
power saving sleep modes.
The ADC generates a 10-bit result which is presented in the ADC data registers, ADCH and
ADCL. By default, the result is presented right adjusted, but can optionally be presented left
adjusted by setting the ADLAR bit in ADCSRB.
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, to ensure that the content of the data
registers belongs to the same conversion. Once ADCL is read, ADC access to data registers
is blocked. This means that if ADCL has been read, and a conversion completes before ADCH
is read, neither register is updated, and the result from the conversion is lost. When ADCH is
read, ADC access to the ADCH and ADCL registers is re-enabled.
The ADC has its own interrupt which can be triggered when a conversion completes. When
ADC access to the data registers is prohibited between reading of ADCH and ADCL, the inter-
rupt will trigger even if the result is lost.
A single conversion is started by writing a logical one to the ADC start conversion bit, ADSC.
This bit stays high as long as the conversion is in progress, and will be cleared by hardware
when the conversion is completed. If a different data channel is selected while a conversion is
in progress, the ADC will finish the current conversion before performing the channel change.
Alternatively, a conversion can be triggered automatically by various sources. Auto triggering
is enabled by setting the ADC auto trigger enable bit (ADATE) in ADCSRA. The trigger source
is selected by setting the ADC trigger select bits (ADTS) in ADCSRB (see the description of
the ADTS bits for a list of the trigger sources). When a positive edge occurs on the selected
trigger signal, the ADC prescaler is reset and a conversion is started. This provides a method
of starting conversions at fixed intervals. If the trigger signal still is set when the conversion
completes, a new conversion will not be started. If another positive edge occurs on the trigger
signal during conversion, the edge will be ignored. Note that an interrupt flag will be set even if
the specific interrupt is disabled or the global interrupt enable bit in SREG is cleared. A conver-
sion can thus be triggered without causing an interrupt. However, the Interrupt Flag must be
cleared in order to trigger a new conversion at the next interrupt event
.
Atmel ATtiny24/44/84 [Preliminary]
139