SE98ATP datasheet(13/43 Pages) NXP

13 / 43 page

SE98A_4

Product data sheet

Rev. 04 — 25 November 2009

13 of 43

NXP Semiconductors

SE98A

DDR memory module temp sensor, 1.7 V to 3.6 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 ‘00’, the location for the Capability register. The Pointer register

latches the last location it was set to. 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 the timing diagrams in Figure 8,

Figure 9, Figure 10 and Figure 11 on how to program the device.

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

Fig 8.

SMBus/I2C-bus write to the Pointer register

123456789123456789

SCL

SDA

device address and write

START

ACK

by device

STOP

ACK

by device

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