Datasheet
SMBUS INTERFACE
Communication Protocols
AMC6821-Q1
SBAS475 – JUNE 2009 ......................................................................................................................................................................................................
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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 V
DD
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
V
DD
GND 0011001
GND NC 0101100
NC NC 0101110
V
DD
NC 0101101
GND V
DD
1001100
NC V
DD
1001110
V
DD
V
DD
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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