Microchip Technology MCP3422, Manual

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MCP3422/3/4
DS22088B-page 22
©
2008 Microchip Technology Inc.
5.3.4 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 config-
uration 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 conver-
sion data (D0).
If the device is configured for 12, 14, or 16 bit-mode, the
device outputs two data bytes followed by a
configuration byte. In 16 bit-conversion mode, the MSB
(= sign bit) of the first data byte is D15. In 14-bit conver-
sion 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 5-4 and 5-5 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.