SE97TP datasheet(13/53 Pages) NXP

13 / 53 page

SE97_6

Product data sheet

Rev. 06 — 17 August 2009

13 of 53

NXP Semiconductors

SE97

DDR memory module temp sensor with integrated SPD, 3.3 V

7.9 SMBus/I2C-bus interface

The data registers in this device are selected by the Pointer register. At power-up, the

Pointer register is set to ‘00h’, the location for the Capability register. The Pointer register

latches the last location to which it was set. Each data register falls into one of three types

of user accessibility:

• Read only

• Write only

• Write/Read same address

A ‘write’ to this device will always include the address byte and the pointer byte. A write to

any register other than the Pointer register requires two data bytes.

Reading this device can take place either of two ways:

• If the location latched in the Pointer register is correct (most of the time it is expected

that the Pointer register will point to one of the Temperature register (as it will be the

data most frequently read), then the read can simply consist of an address byte,

followed by retrieving the two data bytes.

• If the Pointer register needs to be set, then an address byte, pointer byte,

repeat START, and another address byte will accomplish a read.

The data byte has the most signiﬁcant bit ﬁrst. At the end of a read, this device can accept

either Acknowledge (ACK) or No Acknowledge (NACK) from the Master (No Acknowledge

is typically used as a signal for the slave that the Master has read its last byte). It takes this

device 125 ms to measure the temperature. Refer to timing diagrams Figure 9 to

Figure 12 for how to program the device.

Fig 8.

How SE97 responds to SMBus ALERT Response Address

Alert Response Address

START bit

read

acknowledge

002aac685

device address

no acknowledge

STOP bit

host NACK and

sends a STOP bit

Slave acknowledges and

sends its slave address.

The last bit of slave address

is hard coded '0'.

master sends a START bit,

ARA and a read command

host detects

SMBus ALERT

A = ACK = Acknowledge bit. W = Write bit = 0. R = Read bit = 1.

Fig 9.

SMBus/I2C-bus write to the Pointer register

123456789123456789

SCL

SDA

device address and write

START

ACK

by device

STOP

ACK

by device

002aab308

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