BQ24721 Datasheet, PDF (43/48 Pages) Texas Instruments – ADVANCED MULTI-CHEMISTRY AND MULTI-CELL SYNCHRONOUS SWITCH-MODE CHARGER AND SYSTEM POWER SELECTOR

bq24721
www.ti.com
SLUS683 – NOVEMBER 2005
VALID WRITE SEQUENCES
The bq24721 will always ACK its own address. If the CMD points to an allowable READ or WRITE data bq24721
writes the command into its command register and send an ACK. If the CMD points to an nonallowed command
bq24721 does NOT write the command into its command register and sends a NACK.
S
hA0
bqA
S
hA0
bqA
hCMD_N
bqN
WORD WRITE
The data is written to a control register at the end of the ACK after the second byte in the sequence. If an word
write sequence is intrupted by a STOP or START, no data is written to the device. The host can cancel a WRITE
by sending a STOP or START before the trailing edge of ACK clock pulse.
S
hA0
bqA
hCMD
bqA
hDATA
bqA
hDATA
bqA
P
VALID READ SEQUENCES
The bq24721 will only ACK its READ address if it occurs following a repeated start where the high SCL clock
time is less then the t_W(H), MAX of 50 µs. Upon receiving hA1, bq24721 outputs 2 bytes of data as indicated by
the preceding command. The command sequence is terminated by a STOP. The START and the STOP both act
as priority interrupts. If the host has been interrupted and is not sure where it left off, it sends a STOP and resets
the bq24721 state machine to the Idle state. Once in idle state, bq24721 ignores all activity on the SCL and SDA
lines until it receives a START. If a read sequence is terminated early by a START or STOP, the entire sequence
must be restarted by the host for valid data.
S
hA0
bqA hCMD bqA
R
hA1
bqA
bqDATA
hA bqDATA hN
P
SMBus WORD READ
A valid Command is required to write to the bq24721, and a valid Command is required to specify the data to be
read. Once a read command is received the register data for the specified command is output to the host.
NONVALID SEQUENCES
START and non-hA0 or non-hA1 Address
A START followed by an address which is not bqA0 or bqA1 is NACKED.
Attempt to Specify Nonallowed Command
If the CMD points to a nonallowed command (reserved registers) , bq24721 sends a NACK back to the host.
Note that bq24721 NACKS whether a stop is sent or not.
S
hA0
bqA
hCMD_N
bqN
S
hA_N
bqN
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