參數(shù)資料
型號: AD7654AST
廠商: ANALOG DEVICES INC
元件分類: ADC
英文描述: Dual 2-Channel Simultaneous Sampling SAR 500 kSPS 16-Bit ADC
中文描述: 4-CH 16-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL/PARALLEL ACCESS, PQFP48
封裝: MS-026-BBC, LQFP-48
文件頁數(shù): 19/24頁
文件大?。?/td> 734K
代理商: AD7654AST
REV. 0
AD7654
–19–
External Discontinuous Clock Data Read after Conversion
This mode is the most recommended of the serial slave modes.
Figure 18 shows the detailed timing diagrams of this method.
After a conversion is complete, indicated by BUSY returning
low, the results of this conversion can be read while both
CS
and
RD
are low. The data from both channels are shifted out,
MSB first, with 32 clock pulses, and is valid on both rising and
falling edge of the clock.
One advantage of this method is that the conversion perfor-
mance is not degraded because there are no voltage transients on
the digital interface during the conversion process.
Another advantage is to be able to read the data at any speed up
to 40 MHz, which accommodates both slow digital host interface
and the fastest serial reading.
Finally, in this mode only, the AD7654 provides a daisy-chain
feature using the RDC/SDIN input pin for cascading multiple
converters together. This feature is useful for reducing component
count and wiring connections when it is desired, as it is for
instance, in isolated multiconverters applications.
An example of the concatenation of two devices is shown in
Figure 19. Simultaneous sampling is possible by using a common
CNVST signal. It should be noted that the RDC/SDIN input is
latched on the edge of SCLK opposite the one used to shift out
the data on SDOUT. Therefore, the MSB of the upstream
converter follows the LSB of the downstream converter on the
next SCLK cycle.
External Clock Data Read during Conversion
Figure 18 shows the detailed timing diagrams of this method.
During a conversion, while both
CS
and
RD
are low, the result
of the previous conversion can be read. The data is shifted out,
MSB first, with 32 clock pulses, and is valid on both rising and
falling edges of the clock. The 32 bits have to be read before the
current conversion is complete. If that is not done, RDERROR
is pulsed high and can be used to interrupt the host interface to
prevent incomplete data reading. There is no daisy-chain fea-
ture in this mode, and RDC/SDIN input should always be tied
either high or low.
To reduce performance degradation due to digital activity, a fast
discontinuous clock is recommended to ensure that all the bits
are read during the first half of the conversion phase. It is also
possible to begin to read the data after conversion and continue
to read the last bits even after a new conversion has been initiated.
CNVST
SDOUT
SCLK
X
CH A D15
1
2
3
31
32
t
3
t
42
t
43
t
44
t
38
t
39
t
23
BUSY
INVSCLK = 0
CS
EXT/
INT
= 1
CH B D0
CH B D1
CH A D13
CH A D14
RD
= 0
EOC
t
10
t
11
t
13
t
12
A/
B
= 1
Figure 18. Slave Serial Data Timing for Reading (Read Previous Conversion during Convert)
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AD7654ASTRL Dual 2-Channel Simultaneous Sampling SAR 500 kSPS 16-Bit ADC
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