Wide Brightness Range

CCFL Backlight Controllers

22

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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

AB

C

D

E

FG

H

I

J

K

SMBDATA

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

AB

C

D

E

FG

H

I

J

SMBDATA

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