PAC1921_16 Datasheet, PDF (24/46 Pages) –

PAC1921
Attempting to communicate with the PAC1921 SMBus
interface with an invalid slave address or invalid proto-
col will result in no response from the device and will
not affect its register contents. Stretching of the SMCLK
signal is supported, provided other devices on the
SMBus control the timing.
5.4 SMBus Protocols
The device supports Send Byte, Read Byte, Write Byte,
Receive Byte, and the Alert Response Address as valid
protocols as shown below.
All of the below protocols use the convention in
Table 5-2.
TABLE 5-2: PROTOCOL FORMAT
Data Sent to Device Data Sent to the Host
# of bits sent
# of bits sent
5.4.1 WRITE BYTE
The Write Byte is used to write one byte of data to the
registers, as shown in Table 5-3.
TABLE 5-3: WRITE BYTE PROTOCOL
START Slave Address WR ACK Register Address
10
YYYY_YYY
0
0
XXh
ACK
0
Register Data
XXh
ACK
0
STOP
01
5.4.2 READ BYTE
The Read Byte protocol is used to read one byte of data
from the registers as shown in Table 5-4.
TABLE 5-4: READ BYTE PROTOCOL
START
Slave
Address
WR
ACK
Register
Address
ACK
1 0 YYYY_YYY 0
0
XXh
0
START
10
Slave
Address
RD
ACK
Register
Data
NACK
YYYY_YYY 1 0
XXh
1
STOP
01
5.4.3 SEND BYTE
The Send Byte protocol is used to set the internal
address register pointer to the correct address location.
No data is transferred during the Send Byte protocol as
shown in Table 5-5.
TABLE 5-5:
START
10
SEND BYTE PROTOCOL
Slave Address
WR
YYYY_YYY
0
ACK
0
Register Address
XXh
ACK
0
STOP
01
DS20005293D-page 24
 2012-2016 Microchip Technology Inc.