AD7709 Analog Devices, AD7709 Datasheet - Page 19

• Manufacturer Part Number: AD7709
• Description: 16-Bit Sigma Delta ADC with Current Sources, Switchable Reference Inputs and I/O Port
• Manufacturer: Analog Devices

Specifications of AD7709

• Resolution (bits): 16bit
• # Chan: 4
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

CONFIGURING THE AD7709
The four user-accessible registers on the AD7709 are accessed via
the serial interface. Communication with any of these registers
is initiated by first writing to the Communications Register. The
AD7709 begins converting on power-up without the need to
write to the registers. The default conditions are used, i.e., the
AD7709 operates at a 19.79 Hz update rate that offers 50 Hz
and 60 Hz rejection.
Figure 10 outlines a flow diagram of the sequence used to
configure all registers after a power-up or reset on the AD7709.
The flowchart shows two methods of determining when it is valid
to read the data register. The first method is hardware polling of
the RDY pin and the second method involves software interrogation
of the RDY bit in the status register. The flowchart details all the
necessary programming steps required to initialize the ADC and
read data from the ADC channel following a power-on or reset.
The steps can be broken down as follows:
1. Configure and initialize the microcontroller or microproces-
REV. A
WRITE TO CONFIGURATION REGISTER TO SELECT
CONFIGURE AND INITIALIZE C/ P SERIAL PORT
WRITE TO COMMUNICATIONS REGISTER SETTING
WRITE TO COMMUNICATIONS REGISTER SETTING
REFERENCE. CURRENT SOURCES AND I/O PORT
sor serial port.
UP NEXT OPERATION TO BE A WRITE TO THE
FILTER REGISTER (WRITE 22H TO REGISTER)
UP NEXT OPERATION TO BE A WRITE TO THE
WRITE TO FILTER REGISTER CONFIRMING
THE INPUT CHANNEL, INPUT RANGE, AND
HARDWARE
READ DATA FROM OUTPUT REGISTER
POLLING
POWER-ON-RESET FOR AD7709
THE REQUIRED UPDATE RATE
CONFIGURATION REGISTER
CAN ALSO BE CONFIGURED
(WRITE 01H TO REGISTER)
START
SOFTWARE
POLLING
Figure 10. Flowchart for Initializing and Reading Data from the AD7709
WRITE TO COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ FROM THE
DATA REGISTER (WRITE 43H TO REGISTER)
READ 16-BIT DATA RESULT
YES
NO
POLL RDY PIN
HARDWARE
ANOTHER
CHANNEL
CHANGE
POLLING
NO
LOW?
READ
END
RDY
–19–
YES
2. Initialize the AD7709 by configuring the following registers:
3. When configuration is complete, the user needs to determine
a) Filter Register to configure the update rate for the channel.
b)Configuration Register to select the input channel to be
YES
Both of these operations consist of a write to the Communi-
cations Register to specify the next operation as a write to a
specified register. Data is then written to this register. When
each sequence is complete, the ADC defaults to waiting for
another write to the Communications Register to specify the
next operation.
when it is valid to read the data from the data register. This is
accomplished either by polling the RDY pin (hardware polling)
or by interrogating the RDY bit in the STATUS register
(software polling). Both are shown in Figure 10.
The AD7709 must be placed in standby mode before the
Filter Register can be written to.
converted, its input range, and reference. This register is also
used to configure internal current sources, power switches,
and I/O port.
WRITE TO COMMUNICATIONS REGISTER SETTING
WRITE TO COMMUNICATIONS REGISTER SETTING
UP NEXT OPERATION TO BE A READ FROM THE
UP NEXT OPERATION TO BE A READ FROM THE
STATUS REGISTER (WRITE 40H TO REGISTER)
DATA REGISTER (WRITE 43H TO REGISTER)
READ 16-BIT DATA RESULT
YES
READ STATUS REGISTER
NO
SOFTWARE
YES
ANOTHER
CHANNEL
POLLING
CHANGE
NO
NO
RDY = 1
READ
END
AD7709
YES