BQ24721 Datasheet, PDF (42/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
SLUS683 – NOVEMBER 2005
Not acknowledge (NACK) from host
Acknowledge (ACK) from bq24721
Not acknowledge (NACK) from bq24721
Repeated Start
STOP
CONDITION
(P)
START
CONDITION
(S)
CONDITION
BIT 7
MSB
BIT 6
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CODE
hN
bqA
bqN
R
BIT 0
LSB
ACKNOWLEDGE
STOP
CONDITION
(hA or bqA)
(P)
SCL
SDA
STOP
CONDITION
(P)
START
CONDITION
(S)
BIT 7
MSB
BIT 6
BIT 0
LSB
NOT
STOP
ACKNOWLEDGE CONDITION
(hN or bqN)
(P)
SCL
SDA
Figure 61.
SMBus READ/WRITE SEQUENCES
The bq24721 supports the standard SMBus Word Write, as well as the SMBus Word READ. The basic SMBus
word read protocol has the following steps:
1. Host sends a start and bq24721 SMBus slave write address
2. bq24721 ACK’s that this is a valid SMBus address and that the bus is configured for write
3. Host sends bq24721 command
4. bq24721 ACK’s that this is a valid command and stores the command for a possible read
5. Host sends a repeated start and bq24721 SMBus slave read address, reconfiguring the bus for read
6. bq24721 ACK’s that this is a valid address and that bus is reconfigured
7. Bus is in read mode, bq24721 starts sending 2 bytes of data chosen by the command.
The SMBus write protocol is similar to the read, without the need for a repeated start and bus being set in write
mode. If the address sent by host is not a valid address , the command is NACKed. The host can complete a
READ or a WRITE sequence with either a STOP or a START. In a WRITE it is not necessary to end each word
WRITE command with a STOP, a START has the same effect (repeated start).
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