User's Manual

MPR series User’s Manual: Draft version 0.95 11/4/04 page 32
Each time power is turned on, the reader proceeds through a set of steps to initialize the tag IC timing.
First, the reader transmits a RESET consisting of 800 ms of CW power. A tag’s “ID’d” flag (telling it that
it was already read by the reader) may survive a RESET, but in other respects the tag returns to its default
state. After the RESET, 8 pulses are used to calibrate the tag internal oscillator to the 2.2 MHz sub-carrier
frequency. Finally, a set of pulses of varying length is transmitted to set the thresholds for distinguishing
between 0, 1, and null, and to signal the tag when to begin its transmission.
In the United States, communications devices operating in unlicensed bands must either use direct-
sequence or frequency-hopping spreading techniques. The MPR series products use pseudo-random
hopping from one frequency to another. The Class 0 protocol does not require the reader to power down
during hops, but the MPR5000 does in order to minimize spurious radiation. Therefore, a RESET /
calibration sequence is necessary after each hop. The time between hops is available for the user to adjust,
although regulations require that the transmitter remain on any given frequency for no longer than 400 ms
at a time. In Europe, revised regulations allowing 10 channels have been promulgated and it is anticipated
that with the passing of time frequency-hopping operation will become the normal means of operation in
most European jurisdictions. European regulations will require that the reader listen before talking: that is,
the reader must check each putative channel for other active transmitters before beginning its own
transmission. Note that the MPR5000/6000/7000 operate at 902-928 MHz and are not approved for use in
Region 1 (European) jurisdictions.
Tags have 10 possible states, roughly corresponding to [startup / calibrate], [global commands], [binary tree
traversal], and [singulated commands]. Each command is 8 bits long, with an additional parity bit provided
for error checking. The tag echoes each bit it receives in order to provide a simple error check and
acknowledgement function. Mandatory commands are:
• ResetIDFlag: resets the identified flag to NOT READ; that is, it forces tags to forget whether they
have been previously inventoried.
• SetNegotiationPage: this curious terminology is used to describe the choice of ID (ID0, 1, or 2)
used for singulation during binary tree traversal.
• SegRegionofOperation: sets the backscatter parameters according to whether the device is
operating under FCC or European regulations.
• ForceDormant: tags receiving this command immediately enter the Dormant state. The Dormant
state is the default tag turn-on state, exited when a RESET is received.
• ForceMute: tags receiving this command immediately enter the Mute state. In the Mute state, the
tags receive data but do not respond until a NULL is received. Tags that have been bypassed
during traversal reside in the Mute state until the next traversal begins.
• Read: Read ID1 or ID2 (ID0, being randomly generated at the time of request, has no enduring
interest and need not be read from the tag).
• Kill: Permanently disables the tag if a valid argument (passcode) is provided.
1.5.4.1.2 EPC Class 1 Summary
In this section we provide a very brief introduction to the operation of class 1 tags. Further information
may be obtained from the document “Candidate Specification 860 MHz – 2500 MHz – Class 1 RFID Air
Interface”, revision 1.02, available from the EPC Global Inc. web site.
Class 1 tags are nominally factory-programmed but the write operation employs the radio interface and
could be performed at manufacture or in the field. It is expected that once the tag is written to, the memory
is locked and further write operations are disallowed. Each tag contains a nominal 64 bit or 96-bit EPC
and a 16 bit cyclic redundancy check (CRC) in non-volatile memory. The CRC is independently re-
calculated by the reader when the EPC is read, and checked against that provided by the tag to check for
errors in the read. Unlike class 0 tags, where the rag responds immediately to each bit sent by the reader,
class 1 tags use a more conventional packet-oriented protocol, with the reader transmitting a packet
containing commands and data, followed by a response by the tag.