User's Manual

PT40 Postal Tag RFID-LSCAN
Page: 4 of 6
In the sleep mode, only the LF receiver is powered up and the total current consumption is less than 5uA. When a LF signal is
detected by the LF receiver, it wakes-up the microcontroller to check if this signal has a valid modulation pattern. The LF field
validation is done by the microcontroller using an RC internal 90 kHz clock at a low current consumption. If a valid excitation
field is recognized, then the microcontroller wakes-up its UHF Transmitter and transmits on the UHF the pre-programmed
messages. When PT40 recognizes a valid S21 / S23 excitation it transmits on UHF messages using S21 format. The PT40
operation and the message content can be programmed using dedicated devices.
The tag transmits a number of messages each time it enters a valid S21 or S23 fields. First transmission is delayed a few ms
depending of the parameter WID that programmed randomly for each tag within the 10 -30 range during the manufacturing
process. Subsequent transmissions are each randomly delayed compared with the preceding one based on a calculation that
involves several random numbers generated internally function of another parameter WSD. This WSD parameter is also
programmed randomly for each tag within the 10 -30 range during the manufacturing process. Repeating the same message a
number of times ensures that, even if multiple tags are excited in the same time, many messages will not collide and at least one
from each tag will be successfully received.
2.2 Valid Excitation Fields
For a field to be valid, it has to have a special pattern called exciter ID. If fields with different exciter ID overlap and a tag moves
from one to another it will transmit WEP number of messages each time it “sees” a new exciter ID.
2.3 Commands and Parameters
The commands and parameters accepted by Postag PT40 are the same as for the Postag PT21 / PT23 and are listed in the RFID
System S21 – Reference Guide, document 950061 rev. 1.
The most used programmable parameters for PT40 are WIP, WRC and WUD. Examples of default parameters’ values that will
fit most applications are:
WUD = “xxxxx” - use this command to program 5 characters of user data
WIP, WRC= their sum represents the number of identical messages to transmit following an excitation. WIP
parameter range is 1 to 20, WRC parameter range is 0 to 10 - default values are 10.
WID = randomly assigned initial delay after an excitation before the first UHF transmission, multiples of 4
ms, range 1-200, default 1. This ensures a randomization of the first transmissions following an (almost) simultaneously
excitation of multiple tags.
WSD = inter-message random delay, range 7 – 15, default 10 (used for calculating the random interval
between two successive UHF transmissions)
2.4 PT40 vs. PT21
The main functional differences between tags model PT40 and PT21 are related to the ExId range of identifiers, the black-out
time, and the direction of maximum LF sensitivity.
2.4.1 ExId range
Postags PT21 recognize and report received ExId with S21 format in the range 0 to 31.
PT40 recognize and report received ExId with S21 format in the range 0 to 31, and with S23 format in the range 0 to 127.
2.4.2 Black-out
Black-out is the minimum time interval between two consecutive excitations which the tag can recognize. Postag PT21 has a
black-out time 10.0 s. For PT40 this blackout time was reduced to about 2-3 s. In situations where we want to re-register a tag
that leaves and re-enters a field with the same exciter ID, the tag has to be out of the field for more than the black out time
duration. This happens for example when you try to excite a tag multiple times using the same exciter, like a Universal
Programmer UP23 box. The tag will not transmit if it enters an LF field but the excitation pattern cannot be recognized (i.e.
overlapping fields or interference).