SEALED ENERGY SYSTEMS
®
13
User Manual
3.3.4. SMBus Host-to-Battery Message Protocol
The Bus Host communicates with the battery pack using one of
three protocols:
•
Write Word
•
Read Word
•
Read Block
3.3.4.1.Write Word
The first byte of a Write Word access is the command code. The
next two Bytes are the data to be written. In this example the master
asserts the slave device address followed by the write bit. The
device acknowledges and the master delivers the command code.
The slave again acknowledges before the master sends the data
word (low byte first). The slave acknowledges each byte according
to the I²C specification, and the entire transaction is finished with a
stop condition.
Write Word Protocol
Write Word Protocol w/PEC
SMBus Host (Master) Smart Battery (Slave)
3.3.4.2.Read Word
Reading data is slightly more complex than writing data. First the
host must write a command to the slave device. Then it must follow
that command with a repeated start condition to denote a read
from that device's address. The slave then returns two bytes of data.
Note that there is not a stop condition before the repeated start
condition, and that a "Not Acknowledge" signifies the end of the
read transfer.
Read Word Protocol
1
7
1
1
8
1
8
1
8
1
1
S
Battery
Address
Wr A
Command
Code
A
Data
Byte
Low
A
Data
Byte
High
A
P
1
7
1
1
8
1
8
1
8
1
8
1 1
S
Battery
Address
Wr A
Command
Code
A
Data
Byte
Low
A
Data
Byte
High
A PEC A P
1
7
1 1
8
1 1
7
1
1
8
1
8
1 1
S
Battery
Address
Wr A
Command
Code
A S
Battery
Address
Rd
A
Data
Byte
Low
A
Data
Byte
High
!A
P
