参数资料
型号: TSC87C51-33CBB
厂商: ATMEL CORP
元件分类: 微控制器/微处理器
英文描述: 8-BIT, OTPROM, 33 MHz, MICROCONTROLLER, PQCC44
封装: PLASTIC, LCC-44
文件页数: 16/80页
文件大小: 5152K
代理商: TSC87C51-33CBB
207
2466T–AVR–07/10
ATmega16(L)
Using the ADC Interrupt Flag as a trigger source makes the ADC start a new conversion as soon
as the ongoing conversion has finished. The ADC then operates in Free Running mode, con-
stantly sampling and updating the ADC Data Register. The first conversion must be started by
writing a logical one to the ADSC bit in ADCSRA. In this mode the ADC will perform successive
conversions independently of whether the ADC Interrupt Flag, ADIF is cleared or not.
If Auto Triggering is enabled, single conversions can be started by writing ADSC in ADCSRA to
one. ADSC can also be used to determine if a conversion is in progress. The ADSC bit will be
read as one during a conversion, independently of how the conversion was started.
Prescaling and
Conversion Timing
Figure 100. ADC Prescaler
By default, the successive approximation circuitry requires an input clock frequency between 50
kHz and 200 kHz to get maximum resolution. If a lower resolution than 10 bits is needed, the
input clock frequency to the ADC can be higher than 200 kHz to get a higher sample rate.
The ADC module contains a prescaler, which generates an acceptable ADC clock frequency
from any CPU frequency above 100 kHz. The prescaling is set by the ADPS bits in ADCSRA.
The prescaler starts counting from the moment the ADC is switched on by setting the ADEN bit
in ADCSRA. The prescaler keeps running for as long as the ADEN bit is set, and is continuously
reset when ADEN is low.
When initiating a single ended conversion by setting the ADSC bit in ADCSRA, the conversion
starts at the following rising edge of the ADC clock cycle. See “Differential Gain Channels” on
page 209 for details on differential conversion timing.
A normal conversion takes 13 ADC clock cycles. The first conversion after the ADC is switched
on (ADEN in ADCSRA is set) takes 25 ADC clock cycles in order to initialize the analog circuitry.
The actual sample-and-hold takes place 1.5 ADC clock cycles after the start of a normal conver-
sion and 13.5 ADC clock cycles after the start of a first conversion. When a conversion is
complete, the result is written to the ADC Data Registers, and ADIF is set. In single conversion
mode, ADSC is cleared simultaneously. The software may then set ADSC again, and a new
conversion will be initiated on the first rising ADC clock edge.
When Auto Triggering is used, the prescaler is reset when the trigger event occurs. This assures
a fixed delay from the trigger event to the start of conversion. In this mode, the sample-and-hold
takes place 2 ADC clock cycles after the rising edge on the trigger source signal. Three addi-
tional CPU clock cycles are used for synchronization logic. When using Differential mode, along
with Auto triggering from a source other than the ADC Conversion Complete, each conversion
7-BIT ADC PRESCALER
ADC CLOCK SOURCE
CK
ADPS0
ADPS1
ADPS2
CK/128
CK/2
CK/4
CK/8
CK/16
CK/32
CK/64
Reset
ADEN
START
相关PDF资料
PDF描述
TSC87C52-33CDB 8-BIT, OTPROM, 33 MHz, MICROCONTROLLER, PQFP44
T89C51RD2-3CVCM 8-BIT, FLASH, 40 MHz, MICROCONTROLLER, PDIP40
TSC87251A1XXX-B16IDB 8-BIT, OTPROM, 16 MHz, MICROCONTROLLER, PQFP44
TSC51C1XXX-A16CD 8-BIT, MROM, 16 MHz, MICROCONTROLLER, PDSO44
TSC80C31-L16CYD 8-BIT, 16 MHz, MICROCONTROLLER, UUC40
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