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SMBUS INTERFACE

Communication Protocols

AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

The AMC6821 communicates through the serial system management bus (SMBus). The AMC6821 is connected

to this bus as a slave device, under the control of a bus master. The AMC6821 has a 7-bit serial bus address

that is programmable by properly connecting the address pins A0 and A1. Table 2 shows the selection of the

AMC6821 slave address. The address selection pins should be either tied directly to VDD or GND. For the NC

condition, they should be unconnected with minimum trace capacitance. Note that the address is checked only

on a reset or power-up condition.

Table 2. AMC6821 Address Select(1)

A0

A1

ADDRESS

GND

GND

0011000

NC

GND

0011010

VDD

GND

0011001

GND

NC

0101100

NC

NC

0101110

VDD

NC

0101101

GND

VDD

1001100

NC

VDD

1001110

VDD

VDD

1001101

(1)

NC = No connection.

The AMC6821 employs four standard SMBus protocols: the send byte, receive byte, write byte, and read byte.

All other operations result in undefined results. Repeated start is not allowed during the read bit.

Table 3. Send Byte

S

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

P

7-bit AMC6821 slave address

8-bit register address

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).

Table 4. Receive Byte

S

SLAVE ADDRESS

RD

ACK

DATA

NACK

P

8-bit data from the register selected

7-bit AMC6821 slave address

previously

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; RD = read (bit value of 1); NACK = not

acknowledged.

Table 5. Write Byte

S

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

DATA

ACK

P

7-bit AMC6821 slave address

8-bit register address

8-bit data written to register

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).

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