參數(shù)資料
型號(hào)： ADUC842BCPZ8-5
廠商： Analog Devices Inc
文件頁(yè)數(shù)： 24/88頁(yè)
文件大小： 0K
描述： IC MCU 8KB FLASH ADC/DAC 56LFCSP
標(biāo)準(zhǔn)包裝： 1
系列： MicroConverter® ADuC8xx
核心處理器： 8052
芯體尺寸： 8-位
速度： 16.78MHz
連通性： I²C，SPI，UART/USART
外圍設(shè)備： DMA，PSM，PWM，溫度傳感器，WDT
輸入/輸出數(shù)： 32
程序存儲(chǔ)器容量： 8KB（8K x 8）
程序存儲(chǔ)器類型： 閃存
RAM 容量： 2.25K x 8
電壓 - 電源 (Vcc/Vdd)： 4.75 V ~ 5.25 V
數(shù)據(jù)轉(zhuǎn)換器： A/D 8x12b，D/A 2x12b
振蕩器型： 內(nèi)部
工作溫度： -40°C ~ 85°C
封裝/外殼： 56-VFQFN 裸露焊盤，CSP
包裝： 托盤
ADuC841/ADuC842/ADuC843
Rev. 0 | Page 30 of 88
The DMA logic operates from the ADC clock and uses pipelin-
ing to perform the ADC conversions and to access the external
memory at the same time. The time it takes to perform one ADC
conversion is called a DMA cycle. The actions performed by the
logic during a typical DMA cycle are shown in Figure 36.
WRITE ADC RESULT
CONVERTED DURING
PREVIOUS DMA CYCLE
READ CHANNEL ID
TO BE CONVERTED DURING
NEXT DMA CYCLE
CONVERT CHANNEL READ DURING PREVIOUS DMA CYCLE
DMA CYCLE
03260-0-035
Figure 36. DMA Cycle
Figure 36 shows that during one DMA cycle, the following
actions are performed by the DMA logic:
1.
An ADC conversion is performed on the channel whose ID
was read during the previous cycle.
2.
The 12-bit result and the channel ID of the conversion
performed in the previous cycle is written to the external
memory.
3.
The ID of the next channel to be converted is read from
external memory.
For the previous example, the complete flow of events is shown
in Figure 36. Because the DMA logic uses pipelining, it takes
three cycles before the first correct result is written out.
Micro Operation during ADC DMA Mode
During ADC DMA mode, the MicroConverter core is free to
continue code execution, including general housekeeping and
communication tasks. However, note that MCU core accesses to
Ports 0 and 2 (which of course are being used by the DMA con-
troller) are gated off during the ADC DMA mode of operation.
This means that even though the instruction that accesses the
external Ports 0 or 2 appears to execute, no data is seen at these
external ports as a result. Note that during DMA to the inter-
nally contained XRAM, Ports 0 and 2 are available for use.
The only case in which the MCU can access XRAM during
DMA is when the internal XRAM is enabled and the section of
RAM to which the DMA ADC results are being written to lies
in an external XRAM. Then the MCU can access the internal
XRAM only. This is also the case for use of the extended stack
pointer.
The MicroConverter core can be configured with an interrupt
to be triggered by the DMA controller when it has finished
filling the requested block of RAM with ADC results, allowing
the service routine for this interrupt to postprocess data without
any real-time timing constraints.
ADC Offset and Gain Calibration Coefficients
The ADuC841/ADuC842/ADuC843 have two ADC calibration
coefficients, one for offset calibration and one for gain calibra-
tion. Both the offset and gain calibration coefficients are 14-bit
words, and are each stored in two registers located in the special
function register (SFR) area. The offset calibration coefficient is
divided into ADCOFSH (six bits) and ADCOFSL (8 bits), and
the gain calibration coefficient is divided into ADCGAINH
(6 bits) and ADCGAINL (8 bits).
The offset calibration coefficient compensates for dc offset
errors in both the ADC and the input signal. Increasing the
offset coefficient compensates for positive offset, and effectively
pushes the ADC transfer function down. Decreasing the offset
coefficient compensates for negative offset, and effectively
pushes the ADC transfer function up. The maximum offset that
can be compensated is typically ±5% of VREF, which equates to
typically ±125 mV with a 2.5 V reference.
Similarly, the gain calibration coefficient compensates for dc
gain errors in both the ADC and the input signal. Increasing the
gain coefficient compensates for a smaller analog input signal
range and scales the ADC transfer function up, effectively
increasing the slope of the transfer function. Decreasing the
gain coefficient compensates for a larger analog input signal
range and scales the ADC transfer function down, effectively
decreasing the slope of the transfer function. The maximum
analog input signal range for which the gain coefficient can
compensate is 1.025
× VREF, and the minimum input range is
0.975
× VREF, which equates to typically ±2.5% of the reference
voltage.
CALIBRATING THE ADC
Two hardware calibration modes are provided, which can be
easily initiated by user software. The ADCCON3 SFR is used to
calibrate the ADC. Bit 1 (typical) and CS3 to CS0 (ADCCON2) set
up the calibration modes.
Device calibration can be initiated to compensate for significant
changes in operating condition frequency, analog input range,
reference voltage, and supply voltages. In this calibration mode,
offset calibration uses internal AGND selected via ADCCON2
register Bits CS3 to CS0 (1011), and gain calibration uses inter-
nal VREF selected by Bits CS3 to CS0 (1100). Offset calibration
should be executed first, followed by gain calibration. System
calibration can be initiated to compensate for both internal and
external system errors. To perform system calibration by using
an external reference, tie the system ground and reference to
any two of the six selectable inputs. Enable external reference
mode (ADCCON1.6). Select the channel connected to AGND
via Bits CS3 to CS0 and perform system offset calibration. Select
the channel connected to VREF via Bits CS3 to CS0 and perform
system gain calibration.
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