AD7710 Analog Devices, AD7710 Datasheet - Page 20

• Manufacturer Part Number: AD7710
• Description: CMOS, 24-Bit Signal Conditioning ADC with Current Source
• Manufacturer: Analog Devices

Specifications of AD7710

• Resolution (bits): 24bit
• # Chan: 2
• Sample Rate: n/a
• Interface: Ser
• Analog Input Type: Diff-Bip,Diff-Uni
• Ain Range: Bip (Vref)/(PGA Gain),Uni (Vref)/(PGA Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: DIP,SOIC

AD7710
Read Operation
Data can be read from either the output register, the control
register, or the calibration registers. A0 determines whether the
data read accesses data from the control register or from the
output/calibration registers. This A0 signal must remain valid
for the duration of the serial read operation. With A0 high, data is
accessed from either the output register or from the calibration
registers. With A0 low, data is accessed from the control register.
The function of the DRDY line is dependent only on the output
update rate of the device and the reading of the output data
register. DRDY goes low when a new data-word is available in
the output data register. It is reset high when the last bit of data
(either 16th bit or 24th bit) is read from the output register. If
data is not read from the output register, the DRDY line will
remain low. The output register will continue to be updated at
the output update rate, but DRDY will not indicate this. A read
from the device in this circumstance will access the most recent
word in the output register. If a new data-word becomes avail-
able to the output register while data is being read from the
output register, DRDY will not indicate this and the new data-
word will be lost to the user. DRDY is not affected by reading
from the control register or the calibration registers.
Data can be accessed from the output data register only when
DRDY is low. If RFS goes low with DRDY high, no data trans-
fer will take place. DRDY does not have any effect on reading
data from the control register or from the calibration registers.
SDATA (O)
DRDY (O)
SCLK (O)
RFS (I)
A0 (I)
Figure 10. Self-Clocking Mode, Output Data Read Operation
t
2
t
4
t
6
t
7
t
MSB
8
–20–
Figure 10 shows a timing diagram for reading from the AD7710
in the self-clocking mode. This read operation shows a read
from the AD7710’s output data register. A read from the control
register or calibration registers is similar, but, in these cases, the
DRDY line is not related to the read function. Depending on
the output update rate, it can go low at any stage in the control/
calibration register read cycle without affecting the read and its
status should be ignored. A read operation from either the con-
trol or calibration registers must always read 24 bits of data
from the respective register.
Figure 10 shows a read operation from the AD7710. For the
timing diagram shown, it is assumed that there is a pull-up
resistor on the SCLK output. With DRDY low, the RFS input
is brought low. RFS going low enables the serial clock of the
AD7710 and also places the MSB of the word 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 final active falling edge of SCLK
clocks out the LSB and this LSB is valid prior to the final active
rising edge of SCLK. Coincident with the next falling edge of
SCLK, DRDY is reset high. DRDY going high turns off the
SCLK and the SDATA outputs. This means that the data hold
time for the LSB is slightly shorter than for all other bits.
t
9
t
10
LSB
THREE-STATE
t
3
t
5
REV. G