Microchip Technology MCP3421EV Data Sheet

DS22003E-page 22

© 2009 Microchip Technology Inc.

The device acknowledges the general call address
(0x00 in the first byte). The meaning of the general call
address is always specified in the second byte. Refer
to 

. The device supports the following two

general calls.

For more information on the general call, or other I

2

C

modes, please refer to the Phillips I

2

C specification.

5.4.1

GENERAL CALL RESET

The general call reset occurs if the second byte is
‘00000110’ (06h). At the acknowledgement of this
byte, the device will abort current conversion and
perform an internal reset similar to a Power-On-Reset
(POR). All configuration and data register bits are reset
to default values. 

5.4.2

GENERAL CALL CONVERSION

The general call conversion occurs if the second byte
is 

‘00001000’ (08h). All devices on the bus initiate a

conversion simultaneously. When the device receives
this command, the configuration will be set to the One-
Shot Conversion mode and a single conversion will be
performed. The PGA and data rate settings are
unchanged with this general call.

  

The I

2

C specification requires that a high-speed mode

device must be ‘activated’ to operate in high-speed
mode. This is done by sending a special address byte
of “00001XXX” following the START bit. The “XXX” bits
are unique to the High-Speed (HS) mode Master. This
byte is referred to as the High-Speed (HS) Master
Mode Code (HSMMC). The MCP3421 device does not
acknowledge this byte. However, upon receiving this
code, the device switches on its HS mode filters and
communicates up to 3.4 MHz on SDA and SCL bus
lines. The device will switch out of the HS mode on the
next STOP condition.

For more information on the HS mode, or other I

2

C

modes, please refer to the Phillips I

2

C specification. 

The I

2

C specification defines the following bus

protocol:

• Data transfer may be initiated only when the bus 

is not busy

• During data transfer, the data line must remain 

stable whenever the clock line is HIGH. Changes 
in the data line while the clock line is HIGH will be 
interpreted as a START or STOP condition

Accordingly, the following bus conditions have been
defined using 

5.6.1

BUS NOT BUSY (A)

Both data and clock lines remain HIGH.

5.6.2

START DATA TRANSFER (B)

A HIGH to LOW transition of the SDA line while the
clock (SCL) is HIGH determines a START condition. All
commands must be preceded by a START condition.

5.6.3

STOP DATA TRANSFER (C)

A LOW to HIGH transition of the SDA line while the
clock (SCL) is HIGH determines a STOP condition. All
operations can be ended with a STOP condition.

5.6.4

DATA VALID (D)

The state of the data line represents valid data when,
after a START condition, the data line is stable for the
duration of the HIGH period of the clock signal.

The data on the line must be changed during the LOW
period of the clock signal. There is one clock pulse per
bit of data.

Each data transfer is initiated with a START condition
and terminated with a STOP condition.

LSB

First Byte

ACK

X

0

0

0

0

0

0

0

0 A

A

X X X X X X X

(General Call Address)

Second Byte

The I

2

C specification does not allow

“00000000” (00h) in the second byte.

S

S

START

ACK

STOP