SE98A Datasheet, PDF (9/43 Pages) NXP Semiconductors – DDR memory module temp sensor, 1.7 V to 3.6 V

NXP Semiconductors
SE98A
DDR memory module temp sensor, 1.7 V to 3.6 V
7.3.2.2 Critical trip
The T_th(crit) temperature setting is programmed in the Critical Alarm Trip register (04h) as
modified by hysteresis as programmed in the Configuration register. When the
temperature reaches the critical temperature value in this register (and EVENT is
enabled), the EVENT output asserts and cannot be de-asserted until the temperature
drops below the critical temperature threshold. The EVENT cannot be cleared through the
Clear EVENT bit (CEVNT) or SMBus ALERT.
The Critical Alarm Trip should always be set above the Upper Boundary Alarm Trip.
• Advisory notification:
– NXP device: Requires one conversion cycle (125 ms) after setting the Alarm
Window before comparing the alarm limit with temperature register to ensure that
there is correct data in the temperature register before comparing with the Alarm
Window and operating EVENT output.
– Competitor devices: Compares the Alarm Window with temperature register at any
time, so they get the EVENT output immediately when new T_th(crit) and
EVENT output are set at the same time.
– Work-around: Wait at least 125 ms before enabling EVENT output (EOCTL = 1).
Intel will change Nehalem BIOS so that T_th(crit) is set for more than 125 ms before
EVENT output is enabled and Event value is checked.
1. Set T_th(crit).
2. Doing something else (make sure that exceeds 125 ms).
3. Enable the EVENT output (EOCTL = 1).
4. Wait 20 µs.
5. Read Event value.
– SE98B will compare Alarm Window and temperature register immediately after
setting.
7.3.3 Event operation modes
7.3.3.1 Comparator mode
In comparator mode, the EVENT output behaves like a window-comparator output that
asserts when the temperature is outside the window (e.g., above the value programmed in
the Upper Boundary Alarm Trip register or below the value programmed in the Lower
Boundary Alarm Trip register or above the Critical Alarm Trip resister if T_th(crit) only is
selected). Reads/writes on the registers do not affect the EVENT output in comparator
mode. The EVENT signal remains asserted until the temperature goes inside the alarm
window or the window thresholds are reprogrammed so that the current temperature is
within the alarm window.
The comparator mode is useful for thermostat-type applications, such as turning on a
cooling fan or triggering a system shutdown when the temperature exceeds a safe
operating range.
7.3.3.2 Interrupt mode
In interrupt mode, EVENT asserts whenever the temperature crosses an alarm window
threshold. After such an event occurs, writing a 1 to the Clear EVENT bit in the
configuration register de-asserts the EVENT output until the next trigger condition occurs.
SE98A_2
Product data sheet
Rev. 02 — 6 August 2009
© NXP B.V. 2009. All rights reserved.
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