AD7712 Datasheet, PDF (22/28 Pages) Analog Devices – LC2MOS Signal Conditioning ADC

AD7712
Figure 13a shows a read operation from the AD7712 where
RFS remains low for the duration of the data word transmission.
With DRDY low, the RFS input is brought low. The input
SCLK signal should be low between read and write operations.
RFS going low places the MSB of the word to be read on the
serial data line. All subsequent data bits are clocked out on a
high to low transition of the serial clock and are valid prior to
the following rising edge of this clock. The penultimate falling
edge of SCLK clocks out the LSB and the final falling edge
resets the DRDY line high. This rising edge of DRDY turns off
the serial data output.
Figure 13b shows a timing diagram for a read operation where
RFS returns high during the transmission of the word and re-
turns low again to access the rest of the data word. Timing
parameters and functions are very similar to that outlined for
Figure 13a, but Figure 13b has a number of additional times to
show timing relationships when RFS returns high in the middle
of transferring a word.
RFS should return high during a low time of SCLK. On the
rising edge of RFS, the SDATA output is turned off. DRDY
remains low and will remain low until all bits of the data word
are read from the AD7712, regardless of the number of times
RFS changes state during the read operation. Depending on the
time between the falling edge of SCLK and the rising edge of
RFS, the next bit (BIT N + 1) may appear on the databus be-
fore RFS goes high. When RFS returns low again, it activates
the SDATA output. When the entire word is transmitted, the
DRDY line will go high, turning off the SDATA output as per
Figure 13a.
DRDY (O)
t ₂₀
t ₂₁
A0 (I)
RFS (I)
SCLK (I)
SDATA (O)
t ₂₂
t ₂₃
t ₂₆
t ₂₈
t ₂₄
t ₂₅
MSB
t ₂₇
t ₂₉
LSB
THREE-STATE
Figure 13a. External Clocking Mode, Output Data Read Operation
DRDY (O)
t ₂₀
A0 (I)
t ₂₂
RFS (I)
SCLK (I)
SDATA (O)
t ₂₆
t ₂₄
t ₂₅
MSB
t ₃₀
t ₂₇
BIT N
t ₃₁
THREE-STATE
t ₂₄
t ₂₅
BIT N+1
Figure 13b. External Clocking Mode, Output Data Read Operation (RFS Returns High During Read Operation)
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