SE98ATP datasheet(12/43 Pages) NXP

12 / 43 page

SE98A_4

Product data sheet

Rev. 04 — 25 November 2009

12 of 43

NXP Semiconductors

SE98A

DDR memory module temp sensor, 1.7 V to 3.6 V

7.7 SMBus Time-out

The SE98A supports the SMBus time-out feature. If the host holds SCL LOW between

25 ms and 35 ms, the SE98A would reset its internal state machine to the bus idle state to

prevent the system bus hang-up. This feature is turned on by default. The SMBus time-out

is disabled by writing a logic 1 to bit 7 of register 22h.

Remark: When SMBus time-out is enabled, the I2C-bus minimum bus speed is limited by

the SMBus time-out timer, and goes down to only 10 kHz.

The SE98A has no SCL driver, so it cannot hold the SCL line LOW.

Remark: SMBus time-out works over the entire supply range of 1.7 V to 3.6 V unless

shutdown bit (SHMD) is set and turns off the oscillator.

7.8 SMBus ALERT

The SE98A supports SMBus ALERT when it is programmed for the Interrupt mode and

when the EVENT polarity bit is set to logic 0. The EVENT pin can be ANDed with other

EVENT or ALERT signals from other slave devices to signal their intention to

communicate with the host controller. When the host detects EVENT or ALERT signal

LOW, it issues an Alert Response Address (ARA) to which a slave device would respond

with its address. When there are multiple slave devices generating an ALERT the SE98A

performs bus arbitration. If it wins the bus, it responds to the ARA and then clears the

EVENT pin.

Remark: Either in comparator mode or when the SE98A crosses the critical temperature,

the host must also read the EVENT status bit and provide remedy to the situation by

bringing the temperature to within the alarm window or below the critical temperature if

that bit is set. Otherwise, the EVENT pin will not get de-asserted.

Remark: In the SE98A, the ARA is set to default ON. However, in the SE98B the ARA will

be set to default OFF since ARA is not anticipated to be used in DDR3 DIMM applications.

Fig 7.

How SE98A responds to SMBus ALERT

Alert Response Address

START bit

read

acknowledge

002aab330

device address

not 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

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