Data Sheet

ManualsBrandsNational Control Devices ManualsIO Expansion & ADCs4-Channel I2C 4-20mA Current Receiver Board w/ I2C Interface

MCP3426/7/8

If the configuration byte is read repeatedly by clocking

continuously after reading the data bytes (i.e., after the

4th byte in the 16-bit conversion mode), the state of the

RDY

bit indicates whether the device is ready with new

conversion result. When the Master finds the RDY bit is

cleared, it can send a not-acknowledge (NAK) bit and

a stop bit to exit the current read operation and send a

new read command for the latest conversion data.

Once the conversion data has been read, the ready bit

toggles to ‘1’ until the next new conversion data is

ready. The conversion data in the output register is

overwritten every time a new conversion is completed.

Figure 5-3 shows an example of writing configuration

conversion data. The user can rewrite the configuration

byte any time for a new setting. Table 5-1 and Tab le 5-

2 show the examples of the configuration bit operation.

5.3 I

C Serial Communications

The device communicates with the Master

(microcontroller) through a serial I

C (Inter-Integrated

Circuit) interface and support standard (100 kbits/sec),

fast (400 kbits/sec) and high-speed (3.4 Mbits/sec)

modes. The serial I

C is a bidirectional 2-wire data bus

communication protocol using open-drain SCL and

SDA lines.

The device can only be addressed as a slave. Once

addressed, it can receive configuration bits with a write

command or transmit the latest conversion results with

a read command. The serial clock pin (SCL) is an input

only and the serial data pin (SDA) is bidirectional. The

Master starts communication by sending a START bit

and terminates the communication by sending a STOP

bit. In read mode, the device releases the SDA line

after receiving NAK and STOP bits.

An example of a hardware connection diagram is

shown in Figure 6-1. More details of the I

C bus

characteristic is described in Section 5.6 “I

C Bus

Characteristics”.

5.3.1 I

C DEVICE ADDRESSING

The first byte after the START bit is always the address

byte of the device, which includes the device code (4

bits), address bits (3 bits), and R/W

bit. The device

code for the devices is 1101, which is programmed at

the factory. The I

C address bits (A2, A1, A0 bits) are

as follows:

• MCP3426: Programmed at factory

• MCP3427 and MCP3428: Progammed by the

user. It is determined by the logic status of the two

external address selection pins on the user’s

application board (Adr0 and Adr1 pins). The

Master must know the Adr0 and Adr1 pin

conditions before sending read or write command.

See Section 5.3.2 “Device Address Bits (A2,

A1, A0) and Address Selection Pins (MCP3427

and MCP3428)” for more details

Figure 5-1 shows the details of the address byte.

The three I

C address bits allow up to eight devices on

the same I

C bus line. The (R/W) bit determines if the

Master device wants to read the conversion data or

write to the Configuration register. If the (R/W) bit is set

(read mode), the device outputs the conversion data in

the following clocks. If the (R/W

) bit is cleared (write

mode), the device expects a configuration byte in the

following clocks. When the device receives the correct

address byte, it outputs an acknowledge bit after the

R/W

bit.

TABLE 5-1: WRITE CONFIGURATION BITS

R/W O/C RDY Operation

000No effect if all other bits remain

the same - operation continues

with the previous settings.

001Initiate One-Shot Conversion.

010Initiate Continuous Conversion.

011Initiate Continuous Conversion.

TABLE 5-2: READ CONFIGURATION BITS

R/W O/C RDY Operation

100New conversion result in One-

Shot conversion mode has just

been read. The RDY

bit remains

low until set by a new write

command.

101One-Shot Conversion is in prog-

ress. The conversion result is not

updated yet. The RDY

bit stays

high until the current conversion

is completed.

110New conversion result in

Continuous Conversion mode

has just been read. The RDY

bit

changes to high after reading the

conversion data.

111The conversion result in

Continuous Conversion mode

was already read. The next new

conversion data is not ready. The

RDY

bit stays high until a new

conversion is completed.