MCP3425 datasheet(17/38 Pages) MICROCHIP

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DS22072B-page 17

MCP3425

5.3.3

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 (= sign bit) of the first

data byte is D15. In 14-bit conversion mode, the first

two bits in the first data byte are repeated MSB bits and

can be ignored, and the 3rd bit (D13) is the MSB (=sign

bit) of the conversion data. In 12-bit conversion mode,

the first four bits are repeated MSB bits and can be

ignored. The 5th bit (D11) of the byte represents the

MSB (= sign bit) of the conversion data. Table 5-3

summarizes the conversion data output of each

conversion mode.

The configuration byte follows the output data bytes.

The device repeatedly outputs the configuration byte

only if the Master sends clocks repeatedly after the

data bytes.

The device terminates the current outputs when it

receives a Not-Acknowledge (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 Master may read the configuration byte to check

the RDY bit condition.The Master may continuously

send clock (SCL) to repeatedly read the configuration

byte (to check the RDY bit status).

Figure 5-3 shows the timing diagrams of the reading.

TABLE 5-3:

OUTPUT CODES OF EACH RESOLUTION OPTION

Conversion

Option

Digital Output Codes

16-bits

D15 ~ D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte. (Note 1)

14-bits

MMD13 ~ D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte. (Note 2)

12-bits

MMMMD11 ~ D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte. (Note 3)

Note 1:

D15 is MSB (= sign bit).

D13 is MSB (= sign bit), M is repeated MSB of the data byte.

D11 is MSB (= sign bit), M is repeated MSB of the data byte.

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