MCP3425 datasheet(13/30 Pages) MICROCHIP

13 / 30 page

DS22072A-page 13

MCP3425

FIGURE 5-1:

MCP3425 Address Byte.

5.3.2

READING DATA FROM THE DEVICE

When the Master sends a read command (R/W = 1),

the MCP3425 outputs the conversion data bytes and

configuration byte. Each byte consists of 8 bits with

one acknowledge (ACK) bit. The ACK bit after the

address byte is issued by the MCP3425 and the ACK

bits after each conversion data bytes are issued by the

Master.

When the device receives a read command, it outputs

two data bytes followed by a configuration register. In

16 bit-conversion mode, the MSB of the first data byte

is the MSB (D15) of the conversion data. In 14-bit con-

version mode, the first two bits in the first data byte can

be ignored (they are the MSB of the conversion data),

and the 3rd bit (D13) is the MSB of the conversion data.

In 12-bit conversion mode, the first four bits can be

ignored (they are the MSB of the conversion data), and

the 5th bit (D11) of the byte represents the MSB of the

conversion data. Table 5-3 shows an example of the

conversion data output of each conversion mode.

The configuration byte follows the output data byte.

The device outputs the configuration byte as long as

the SCL pulses are received. The device terminates

the current outputs when it receives a Not-Acknowl-

edge (NAK), a repeated start or a stop bit at any time

during the output bit stream. It is not required to read

the configuration byte. However, the user may read the

configuration byte to check the RDY bit condition to

confirm whether the just received data bytes are

updated conversion data. The user may continuously

send clock (SCL) to repeatedly read the configuration

bytes to check the RDY bit status.

Figures 5-2 and 5-2 show the timing diagrams of the

reading.

5.3.3

WRITING A CONFIGURATION BYTE

TO THE DEVICE

When the Master sends an address byte with the R/W

bit low (R/W = 0), the MCP3425 expects one

configuration byte following the address. Any byte sent

after this second byte will be ignored. The user can

change the operating mode of the device by writing the

configuration register bits.

If the device receives a write command with a new

configuration setting, the device immediately begins a

new conversion and updates the conversion data.

Start bit

Read/Write bit

Address Byte

R/W ACK

Device Code

Address Bits (Note 1)

Address

Acknowledge bit

Address

Note

Specified by customer and programmed at the

factory. If not specified by the customer,

programmed to ‘000’.

TABLE 5-3:

EXAMPLE OF CONVERSION DATA OUTPUT OF EACH CONVERSION MODE

Conversion

Mode

Conversion Data Output

16-bits

MD14~D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte

14-bits

MMMD12~D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte

12-bits

MMMMMD10D9D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte

Note:

M is MSB of the data byte.

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