MCP3421 Microchip Technology, MCP3421 Datasheet - Page 13

• Manufacturer Part Number: MCP3421
• Description: 18-Bit Analog-to-Digital Converter with I2C Interface and On-Board Reference
• Manufacturer: Microchip Technology

FIGURE 5-1:
5.3.2
When the Master sends a read command (R/W = 1),
the MCP3421 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 MCP3421 and the ACK
bits after each conversion data bytes are issued by the
Master.
When the device is configured for 18-bit conversion
mode, the device outputs three data bytes followed by
a configuration byte. The first 7 data bits in the first
data byte are the MSB 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 by a
configuration byte. In 16 bit-conversion mode, the MSB
of the first data byte is the MSB (D15) of the conversion
data. In 14-bit conversion 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
TABLE 5-3:
© 2006 Microchip Technology Inc.
Conversion
Note 1:
Note:
18-bits
16-bits
14-bits
12-bits
Mode
Start bit
1
READING DATA FROM THE DEVICE
M is MSB of the data byte.
Specified by customer and programmed at the
factory. If not specified by the customer,
programmed to ‘
Device Code
1
MMMMMMMD16 (1st data byte) - D15 ~ D8 (2nd data byte) - D7 ~ D0 (3rd data byte) - Configuration
byte
MD14~D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte
MMMD12~D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte
MMMMMD10D9D8 (1st data byte) - D7 ~ D0 (2nd data byte) - Configuration byte
EXAMPLE OF CONVERSION DATA OUTPUT OF EACH CONVERSION MODE
0
Address
Address Byte
Address
MCP3421 Address Byte.
1
000
Address Bits
X
’.
Read/Write bit
X
Acknowledge bit
X
(Note 1)
R/W ACK
Conversion Data Output
represents the MSB of the conversion data.
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 5-3 show the timing diagrams of the
reading.
5.3.3
When the Master sends an address byte with the R/W
bit low (R/W = 0), the MCP3421 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.
WRITING A CONFIGURATION BYTE
TO THE DEVICE
MCP3421
DS22003B-page 13
Table 5-3