LTC4302CMS-2 datasheet(13/20 Pages) LINER

13 / 20 page

LTC4302-1/LTC4302-2

sn430212 430212fs

Data Transfer Timing for Write Commands

In order to help ensure that bad data is not written into the

LTC4302, data from a write command is only stored after

a valid Stop Bit has been performed. If a Start Bit occurs

after new data bytes have been written but before a Stop

Bit is issued, the new data bytes are lost. In this case, the

master must readdress the part, rewrite the data bytes and

issue a Stop Bit before issuing any Start Bits to properly

update the registers. Also note that driving the CONN pin

low asynchronously resets the registers to their default

states, as specified in Tables 2 and 3. When CONN is driven

back high, the registers remain in the default state.

Reading from the LTC4302

The LTC4302 can be read using three different formats, as

shown in Figures 7 through 9. Each format begins with a

Start Bit, followed by the Address Byte, as discussed

above. The procedure for reading one data byte is given by

the SMBus Receive Byte protocol, illustrated in Figure 7.

The bits of the Data Byte are read from the LTC4302’s

bits. While only the first 3 bits of Register 1 can be written,

the first 5 bits contain useful information to be read. The

two added bits indicate the logic state of the GPIO pins.

The 3 LSBs are not used and are always “000.”

The format for reading two data bytes is shown in Figure

8. The Address Byte and first Data Byte are exactly the

same as they are for the Receive Byte protocol. After the

first Data Byte, the master transmits an Acknowledge

indicating that it wants to read another data byte. The bits

contained in Register 2 are then written onto the bus as

“Data Byte 2.” Table 3 defines the functions of these

control bits. The 2 LSB’s are not used and are always “11.”

The master signals a not acknowledge after the last

byte read.

The SMBus Read Word protocol can also be used to read

two bytes from the LTC4302, as shown in Figure 9. Note

that the first Address Byte and the Command Code consti-

tute a write operation. However, because these bytes are

followed immediately by a Start Bit and not a Stop Bit, the

data contained in the Command Code is not written into

the LTC4302. After the second Start Bit, the format is

exactly the same as shown in Figure 8.

OPERATIO

START

ACK

11 a4 - a0

XXXXXXXX

ACK

COMMAND

CODE

SLAVE

ADDRESS

START

ACK

11 a4 - a0

d7 - d3 000

ACK

DATA

BYTE 1

d7 - d2 11

STOP

DATA

BYTE 2

SLAVE

ADDRESS

4302 F09

ACK

Figure 9. Reading Two Bytes Using SMBus Read Word Protocol

START

ACK

11 a4 - a0

d7 - d3 000

ACK

DATA

BYTE

SLAVE

ADDRESS

STOP

4302 F07

Figure 7. Reading One Byte Using Receive Byte Protocol

START

ACK

11 a4 - a0

d7 - d3 000

ACK

DATA

BYTE 1

d7 - d2 11

DATA

BYTE 2

SLAVE

ADDRESS

STOP

4302 F08

ACK

Figure 8. Reading Two Bytes

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