SPSXT001
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4
Temperature Sensor Functions
Temperature Requests
The Magnus−S3 includes a precise temperature−sensing
circuit. The circuit generates a TEMPERATURE CODE
when it receives a Temperature Request command. The
TEMPERATURE CODE is a 12−bit number which can be
converted to temperature reading.
The temperature−sensing circuit runs in response to a
Temperature Request, which is a standard SELECT
command with the parameters given below:
• MemBank set to 0x3 (11b)
• The Temperature Sensing Enable address (0xE0) in the
Pointer field
• Length set to 0x0 (a zero length Mask)
• Mask field empty
The highest precision is achieved when the Temperature
Request is followed by 2.5 ms of continuous wave output
from the reader before any subsequent commands are sent.
This provides time to complete and store the
TEMPERATURE CODE in the TEMPERATURE CODE
register in the RESERVED Memory Bank.
Reading the Temperature Code
The TEMPERATURE CODE is a 12−bit value, stored in
the least significant bits from 0xE0 to 0xEF in the Reserved
Memory Bank. This value can be accessed with a standard
READ command. Higher TEMPERATURE CODE values
correspond to higher temperatures. The TEMPERATURE
CODE is converted to a precise temperature measurement
with a linear mapping characterized by the
equation: T = aC + b. T is the temperature in °C. C is the
TEMPERATURE CODE read from the sensor. The a and b
constants are custom to each chip. For more details on the
temperature calibration procedure, please refer to
Application Note AND9213.
Temperature Calibration Data
Magnus−S3 chips come with temperature calibration data
stored in the User Memory Bank in addresses 0x80 through
0xBF. This data is generated from a single−point calibration
conducted on each chip during manufacturing. If greater
precision is desired, the user can calibrate the chip at a
second temperature, and add this to the existing calibration
data.
On−Chip RSSI Code
Magnus−S3 incorporates circuitry that measures
incoming signal strength and converts it to a digital value:
the On−Chip RSSI (Received Signal Strength Indicator)
Code. This can be communicated to a reader and used for
control purposes. The On−Chip RSSI Code has a 32−level
range, represented by a 5−bit number.
The On−Chip RSSI Code, in word D0
h
−DF
h
in the
Reserved Bank, will be returned as the 5 LSBs of a response
to a standard READ command specifying word address D
h
.
Magnus−S3 must first receive an On−Chip RSSI Request
before the On−Chip RSSI Code becomes available.
On−Chip RSSI Requests
On−Chip RSSI Request is a tool for a reader to specify that
it wants to hear only from tags that are seeing a desired
amount of received signal strength. It allows a reader to limit
its communications only to nearby tags – or conversely, to
“mute” nearby tags in order to attempt communication with
tags receiving weak signals.
The On−Chip RSSI Threshold “address” (A0
h
of the User
Bank) is used only by Magnus−S3 to interpret a SELECT
command and is not an actual memory location. It is sent by
the reader using a standard Gen 2 SELECT command. The
6−bits of On−Chip RSSI Threshold Value/Control are
communicated as part of the Mask sent to the tags.
The list below from the Gen 2 version 2.0.0 spec shows the
format of a SELECT command. To send an On−Chip RSSI
Request, the reader issues a SELECT command with:
• MemBank set to 3
h
(11
b
)
• The On−Chip RSSI Threshold address (A0
h
) in the
Pointer field
• Length set to 00001000
b
(the On−Chip RSSI request
value consists of the lower 6 bits of an 8−bit Mask)
• The On−Chip RSSI request in the lower 6 bits of the
Mask, consisting of a leading bit for control followed
by 5 bits for the On−Chip RSSI Code at which the
reader wants to define the tags’ response/no−response
threshold.
The control bit determines whether the threshold value is
interpreted by Magnus−S3 as a lower or upper threshold.
Specifically, if the control bit is set to 0, it will respond if its
internally generated On−Chip RSSI Code is less than or
equal to the threshold value. If the control bit is 1, it will
respond if its On−Chip RSSI Code is greater than the
threshold.
ORDERING INFORMATION
Device Feature UHF Band Attach Material Package Shipping
SPS1T001PET Moisture FCC
902−928 MHz
Non−metal Case 888AF 1000 / Reel
SPS2T001PET Moisture ETSI
866−868 MHz
Non−metal Case 888AG 1000 / Reel
