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AD7719

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CONFIGURING THE AD7719

All user-accessible registers on the AD7719 are accessed via the

serial interface. Communication with any of these registers is

initiated by first writing to the Communications Register.

Figure 11 outlines a flow diagram of the sequence used to con-

figure all registers after a power-up or reset on the AD7719. The

flowchart shows two methods of determining when it is valid to

read the data register or determine when a calibration cycle is

complete. The first method is hardware polling of the RDY

pin and the second method involves software interrogation of

bits in the status and mode registers. The flowchart details all the

necessary programming steps required to initialize the ADC and

read data from the main and aux channel following a power-on or

reset. The steps can be broken down as follows:

1. Configure and initialize the microcontroller or microprocessor

serial port.

2. Initialize the AD7719 by configuring the following registers:

a) IOCON to configure the current sources and digital I/O

port.

b) FILTER to configure the update rate for both channels.

c) AD1CON to enable the aux channel, select the analog

input, select unipolar or bipolar operation and input range.

d) AD0CON to enable the Main ADC channel and select

16-/24-bit mode, analog input range and either unipolar

or bipolar operation.

e) MODE to configure the operating mode. Operating mode

consists of calibration or conversion.

All of these operations consist of a write to the communica-

tions 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.

3. When the operating mode is selected, the user needs to deter-

mine when its valid to read the data in conversion mode or

when the calibration is complete in calibration mode. This is

accomplished either by polling the RDY pin (hardware poll-

ing) or by interrogating the bits in either the STATUS or

MODE registers (software polling). Both are shown in Figure

11. It is assumed that both the main and aux ADCs are being

used and calibration required. If the AD7719 is operated at

the factory-calibrated conditions, a field calibration will not be

required and these steps can be bypassed.

MICROCOMPUTER/MICROPROCESSOR INTERFACING

The AD7719’s flexible serial interface allows for easy interface

to most microcomputers and microprocessors. The flowchart of

Figure 11 outlines the sequence that should be followed when

interfacing a microcontroller or microprocessor to the AD7719.

Figures 12, 13, and 14 show some typical interface circuits.

The serial interface on the AD7719 is capable of operating from

just three wires and is compatible with SPI interface protocols.

The 3-wire operation makes the part ideal for isolated systems

where minimizing the number of interface lines minimizes the

number of opto-isolators required in the system. The serial

clock input is a Schmitt-triggered input to accommodate slow

edges from optocouplers. The rise and fall times of other digital

inputs to the AD7719 should be no longer than 1

µs.

Most of the registers on the AD7719 are 8-bit registers, which

facilitates easy interfacing to the 8-bit serial ports of microcon-

trollers. The Main Channel Data Register (AD0) on the AD7719

can be either 16 or 24 bits, the aux ADC data register (AD1) is

16 bits wide and the offset and gain registers are 24-bit registers,

but data transfers to these registers can consist of multiple 8-bit

transfers to the serial port of the microcontroller. DSP proces-

sors and microprocessors generally transfer 16 bits of data in a

serial data operation. Some of these processors, such as the

ADSP-2105, have the facility to program the amount of cycles

in a serial transfer. This allows the user to tailor the number of

bits in any transfer to match the register length of the required

Even though some of the registers on the AD7719 are only eight

bits in length, communicating with two of these registers in

successive write operations can be handled as a single 16-bit

data transfer if required. For example, if the Filter Register is to

be updated, the processor must first write to the Communications

required, this can all be done in a single 16-bit transfer because

once the eight serial clocks of the write operation to the Commu-

nications Register have been completed, the part immediately

sets itself up for a write operation to the Setup Register.

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