Temperature Sensor with SPD EEPROM Operation
Thermal Sensor Operations
The integrated thermal sensor continuously monitors the temperature of the module
PCB directly below the device and updates the temperature data register. Temperature
data may be read from the bus host at any time, which provides the host real-time feed-
back of the module's temperature. Multiple programmable and read-only temperature
registers can be used to create a custom temperature-sensing solution based on system
requirements and JEDEC JC-42.2.
EVENT_n Pin
The temperature sensor also adds the EVENT_n pin (open-drain), which requires a pull-
up to V
DDSPD
. EVENT_n is a temperature sensor output used to flag critical events that
can be set up in the sensor’s configuration registers. EVENT_n is not used by the serial
presence-detect (SPD) EEPROM.
EVENT_n has three defined modes of operation: interrupt, comparator, and TCRIT. In
interrupt mode, the EVENT_n pin remains asserted until it is released by writing a 1 to
the clear event bit in the status register. In comparator mode, the EVENT_n pin clears
itself when the error condition is removed. Comparator mode is always used when the
temperature is compared against the TCRIT limit. In TCRIT only mode, the EVENT_n
pin is only asserted if the measured temperature exceeds the TCRIT limit; it then re-
mains asserted until the temperature drops below the TCRIT limit minus the TCRIT
hysteresis.
SPD EEPROM Operation
DDR4 SDRAM modules incorporate SPD. The SPD data is stored in a 512-byte, JEDEC
JC-42.4-compliant EEPROM that is segregated into four 128-byte, write-protectable
blocks. The SPD content is aligned with these blocks as shown in the table below.
Block Range Description
0 0–127 000h–07Fh Configuration and DRAM parameters
1 128–255 080h–0FFh Module parameters
2 256–319 100h–13Fh Reserved (all bytes coded as 00h)
320–383 140h–17Fh Manufacturing information
3 384–511 180h–1FFh End-user programmable
The first 384 bytes are programmed by Micron to comply with JEDEC standard JC-45,
"Appendix X: Serial Presence Detect (SPD) for DDR4 SDRAM Modules." The remaining
128 bytes of storage are available for use by the customer.
The EEPROM resides on a two-wire I
2
C serial interface and is not integrated with the
memory bus in any manner. It operates as a slave device in the I
2
C bus protocol, with all
operations synchronized by the serial clock. Transfer rates of up to 1 MHz are achieva-
ble at 2.5V (NOM).
Micron implements reversible software write protection on DDR4 SDRAM-based mod-
ules. This prevents the lower 384 bytes (bytes 0 to 383) from being inadvertently pro-
grammed or corrupted. The upper 128 bytes remain available for customer use and are
unprotected.
16GB (x72, ECC, SR) 288-Pin DDR4 RDIMM
Temperature Sensor with SPD EEPROM Operation
09005aef8630c9f3
asf18c2gx72pz.pdf - Rev. D 8/16 EN
13
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