Rainbow Electronics MAX1839 - Manual (Page 22)

MAX1739/MAX1839
†
Wide Brightness Range
CCFL Backlight Controllers
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be used to read or write the brightness, SHMD, status,
or ID registers.
Table 6 summarizes the command byte’s register
assignments, as well as each register’s power-on state.
The MAX1739 also supports the receive-byte protocol
for quicker data transfers. This protocol accesses the
register configuration pointed to by the last command
byte. Immediately after power-up, the data byte
returned by the receive-byte protocol is the contents of
the brightness register, left justified (i.e., BRIGHT4 will
be in the MSB position of the data byte) with the
remaining bits containing a 1, STATUS1, and STATUS0.
This gives the same result as using the read-byte proto-
col with a 0b10XXXXXX (0x80) command. Use caution
with shorter protocols in multimaster systems since a
second master could overwrite the command byte with-
out informing the first master. During shutdown, the ser-
ial interface remains fully functional. The part also
supports limited read/write-word protocol. Read-word
works similar to read-byte except the second byte
returned is 0xFF. Write-word also works similar to write-
byte. The second data byte is acknowledged and
updated after the first data byte is acknowledged and
updated.
SMBCLK
A B C D E F G H I J K
SMBDATA
t
SU:STA
t HD:STA
t LOW t HIGH
t
SU:DAT
t
HD:DAT
t
HD:DAT t SU:STO t
BUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
L M
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Figure 12. SMBus Write Timing
SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
A B C D E F G H I J
SMBDATA
t SU:STA t HD:STA
t LOW t HIGH
t SU:DAT t HD:DAT t SU:DAT t SU:STO t BUF
K
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
Figure 13. SMBus Read Timing