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AD7414/AD7415

Rev. F | Page 12 of 20

SERIAL INTERFACE

Control of the AD7414/AD7415 is carried out via the I2C-

compatible serial bus. The AD7414/AD7415 are connected to

this bus as slave device, under the control of a master device,

such as the processor.

SERIAL BUS ADDRESS

Like all I2C-compatible devices, the AD7414/AD7415 have a

7-bit serial address. The four MSBs of this address for the

AD7414/AD7415 are set to 1001. The AD7414/AD7415 are

available in four versions: AD7414/AD7415-0, AD7414/

AD7415-1, AD7414-2, and AD7414-3. The first two versions

have three different I2C addresses available, which are selected

by either tying the AS pin to GND, to VDD, or letting the pin

float (see Table 4). By giving different addresses for the four

versions, up to eight AD7414s or six AD7415s can be connected

to a single serial bus, or the addresses can be set to avoid

conflicts with other devices on the bus.

The serial bus protocol operates as follows.

The master initiates data transfer by establishing a START

condition, defined as a high-to-low transition on the serial data

line SDA, while the serial clock line SCL remains high. This

indicates that an address/data stream follows. All slave periph-

erals connected to the serial bus respond to the START condi-

tion and shift in the next eight bits, consisting of a 7-bit address

(MSB first) plus an R/W bit, which determines the direction of

the data transfer and whether data is written to or read from the

slave device.

The peripheral whose address corresponds to the transmitted

address responds by pulling the data line low during the low

period before the ninth clock pulse, known as the acknowledge

bit. All other devices on the bus remain idle while the selected

device waits for data to be read from or written to it. If the R/W

bit is 0, the master writes to the slave device. If the R/W bit is 1,

the master reads from the slave device.

Data is sent over the serial bus in sequences of nine clock

pulses, eight bits of data followed by an acknowledge bit from

the receiver of data. Transitions on the data line must occur

during the low period of the clock signal and remain stable

during the high period, because a low-to-high transition when

the clock is high may be interpreted as a STOP signal.

When all data bytes have been read or written, stop conditions

are established. In WRITE mode, the master pulls the data line

high during the 10th clock pulse to assert a STOP condition. In

READ mode, the master device pulls the data line high during

the low period before the ninth clock pulse. This is known as

No Acknowledge. The master then takes the data line low

during the low period before the 10th clock pulse, then high

during the 10th clock pulse to assert a STOP condition.

Any number of bytes of data may be transferred over the serial

bus in one operation, but it is not possible to mix read and write

in one operation. The type of operation is determined at the

beginning and cannot then be changed without starting a new

operation.

WRITE MODE

Depending on the register being written to, there are two

different writes for the AD7414/AD7415.

Writing to the Address Pointer Register for a Subsequent

Read

In order to read data from a particular register, the address

pointer register must contain the address of that register. If it

does not, the correct address must be written to the address

pointer register by performing a single-byte write operation, as

shown in Figure 10. The write operation consists of the serial

bus address followed by the address pointer byte. No data is

written to any of the data registers. A read operation is then

performed to read the register.

Writing a Single Byte of Data to the Configuration

All three registers are 8-bit registers, so only one byte of data

can be written to each register. Writing a single byte of data to

one of these registers consists of the serial bus address, the data

by the data byte written to the selected data register. This is

illustrated in Figure 11.

READ MODE

Reading data from the AD7414/AD7415 is a 1- or 2-byte

operation. Reading back the contents of the configuration

read operation, as shown in Figure 12. The register address was

previously set up by a single-byte write operation to the address

pointer register. Once the register address has been set up, any

number of reads can subsequently be performed from that

again. To read from another register, the address pointer

address.

Reading data from the temperature value register is a 2-byte

operation, as shown in Figure 13. The same rules apply for a

2-byte read as a 1-byte read.

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