LTC2450 datasheet(17/34 Pages) AD

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LTC2945

Rev. C

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APPLICATIONS INFORMATION

Stuck-Bus Reset

The LTC2945 I2C interface features a stuck bus reset timer

to prevent it from holding the bus lines low indefinitely if

the SCL signal is interrupted during a transfer. The timer

starts when either SCL or SDAI is low, and resets when

both SCL and SDAI are pulled high. If either SCL or SDAI

are low for over 33ms, the stuck-bus timer will expire and

the internal I2C interface and the SDAO pin pulldown logic

will be reset to release the bus. Normal communication

will resume at the next Start command.

Acknowledge

The acknowledge signal is used for handshaking between

the transmitter and the receiver to indicate that the last

byte of data was received. The transmitter always releases

the SDA line during the acknowledge clock pulse. The

LTC2945 will pull the SDA line low on the 9th clock cycle

to acknowledge receipt of the data. If the slave fails to

acknowledge by leaving SDA high, then the master can

abort the transmission by generating a Stop condition.

When the master is receiving data from the slave, the

master must acknowledge the slave by pulling down the

SDA line during the 9th clock pulse to indicate receipt of

a data byte. After the last byte has been received by the

master, it will leave the SDA line high (not acknowledge)

and issue a Stop condition to terminate the transmission.

Write Protocol

The master begins a write operation with a Start condition

followed by the seven-bit slave address and the R/W bit

set to zero. After the addressed LTC2945 acknowledges

the address byte, the master then sends a command byte

that indicates which internal register the master wishes to

write. The LTC2945 acknowledges this and then latches the

lower six bits of the command byte into its internal register

address pointer. The master then delivers the data byte and

the LTC2945 acknowledges once more and writes the data

into the internal register pointed to by the register address

pointer. If the master continues sending additional data

bytes with a Write Word or extended Write command, the

additional data bytes will be acknowledged by the LTC2945,

the register address pointer will automatically increment by

one, and data will be written as above. The write operation

terminates and the register address pointer resets to 00h

when the master sends a Stop condition.

Read Protocol

The master begins a read operation with a Start condition

followed by the 7-bit slave address and the R/W bit set

to zero. After the addressed LTC2945 acknowledges the

address byte, the master then sends a command byte

that indicates which internal register the master wishes

to read. The LTC2945 acknowledges this and then latches

the lower six bits of the command byte into its internal

Start condition followed by the same 7-bit address with

the R/W bit now set to 1. The LTC2945 acknowledges

and sends the contents of the requested register. The

transmission terminates when the master sends a Stop

condition. If the master acknowledges the transmitted

data byte, as in a Read Word command, the LTC2945 will

send the contents of the next register. If the master keeps

acknowledging, the LTC2945 will keep incrementing the

read operation terminates and the register address pointer

resets to 00h when the master sends a Stop condition.

Alert Response Protocol

When any of the fault bits in the FAULT register are set, a

bus alert is generated if the appropriate bit in the ALERT

which faults will generate alerts. At power-up, the ALERT

high. If an alert is enabled, the corresponding fault causes

the ALERT pin to pull low. The bus master responds to the

alert in accordance with the SMBus alert response protocol

by broadcasting the Alert Response Address (0001100)b,

and the LTC2945 replies with its own address and releases

its ALERT pin as shown in Figure 13. The ALERT line is also

released if the FAULT or FAULT CoR registers are read (see

Table 2) since the faulting event can be identified by the

content in these registers. The ALERT signal is not pulled

low again until the Fault register indicates a different fault

has occurred or the original fault is cleared and it occurs

again. Note that this means repeated or continuing faults

will not generate additional alerts until the associated FAULT

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