MCP3421 datasheet(19/42 Pages) MICROCHIP

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DS22003E-page 19

MCP3421

5.3.3

READING OUTPUT CODES AND

CONFIGURATION BYTE FROM THE

DEVICE

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

the device outputs both the conversion data and config-

uration bytes. Each byte consists of 8 bits with one

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

byte is issued by the device and the ACK bits after each

conversion data bytes are issued by the Master.

When the device is configured for 18-bit conversion

mode, it outputs three data bytes followed by a

configuration byte. The first 6 data bits in the first data

byte are repeated MSB (= sign bit) of the conversion

data. The user can ignore the first 6 data bits, and take

the 7th data bit (D17) as the MSB of the conversion

data. The LSB of the 3rd data byte is the LSB of the

conversion data (D0).

If the device is configured for 12, 14, or 16 bit-mode, the

device

outputs

two

data

bytes

followed

configuration byte. 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).

Figures 5-3 and 5-4 show the timing diagrams of the

reading.

TABLE 5-3:

OUTPUT CODES OF EACH RESOLUTION OPTION

Conversion

Option

Digital Output Codes

18-bits

MMMMMMD17D16 (1st data byte) - D15 ~ D8 (2nd data byte) - D7 ~ D0 (3rd data byte) - Configuration

byte.

(Note 1)

16-bits

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

(Note 2)

14-bits

MMD13D ~ D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte.

(Note 3)

12-bits

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

(Note 4)

Note 1: D17 is MSB (= sign bit), M is repeated MSB of the data byte.

2: D15 is MSB (= sign bit).

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

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

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