ISL97635A datasheet(17/29 Pages) RENESAS

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ISL97635A

FN6564 Rev.3.00

Page 17 of 29

Sep 26, 2017

Write Byte

The Write Byte protocol is only three bytes long. The first byte starts

with the slave address followed by the “command code,” which

translates to the “register index” being written. The third byte

contains the data byte that must be written into the register selected

by the “command code”. A shaded label is used on cycles during

which the slaved backlight controller “owns” or “drives” the Data

line. All other cycles are driven by the “host master.”

Read Byte

As shown in the Figure 22, the 4 byte long Read Byte protocol starts

out with the slave address followed by the “command code” which

translates to the “register index.” Then the bus direction turns

around with the re-broadcast of the slave address with Bit 0

indicating a read (“R”) cycle. The fourth byte contains the data being

returned by the backlight controller. That byte value in the data byte

reflects the value of the register being queried at the “command

code” index. Note the bus directions, which are highlighted by the

shaded label that is used on cycles during which the slaved

backlight controller “owns” or “drives” the Data line. All other cycles

are driven by the “host master.”

Slave Device Address

The slave address contains in 7 MSB plus one LSB as R/W bit but

these 8 bits are usually called slave address byte. As shown in

Figure 23, the high nibble of the slave address byte is 0x5 or 0101b

to denote the “backlight controller class.” Bit 3 in the lower nibble of

the slave address byte is 1. Bit 0 is always the R/W bit, as specified

by the SMBus protocol. Note: In this document, the device address

will always be expressed as a full 8-bit address instead of the shorter

7-bit address typically used in other backlight controller

specifications to avoid confusion. Therefore, if the device is in the

write mode where Bit 0 is 0, the slave address byte is 0x58 or

01011000b. If the device is in the read mode where Bit 0 is 1, the

slave address byte is 0x59 or 01011001b.

The backlight controller may sense the state of the pins at POR or

during normal operation—the pins will not change state while the

device is in operation.

181

SLAVE ADDRESS

COMMAND CODE

ADATA BYTE

FIGURE 21. WRITE BYTE PROTOCOL

Slave to Master

Master to Slave

FIGURE 22. READ BYTE PROTOCOL

181

SSLAVE ADDRESS

ACOMMAND CODE

SLAVE ADDRESS

DATA BYTE

Slave to Master

Master to Slave

FIGURE 23. SLAVE ADDRESS BYTE DEFINITION

DEVICE

IDENTIFIER

DEVICE

ADDRESS

MSB

LSB

101100

R/W

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