R
EM4223
BEGIN_ROUND COMMAND SELECTION OPERATION
(see Fig. 19)
The BEGIN_ROUND command contains 2 selection
parameters. The 1st parameter, called MASK_LENGTH,
consists of a fixed length (8 bit) value, which specifies
how many bits will be sent in the following parameter,
called the MASK. This MASK_LENGTH will be between
0 and 136 for the EM4223. The MASK value will be
compared to the number of bits of the tags data memory
The MASK value is transmitted MSB 1st. The 1st bit of the
MASK is compared to the MSB of the Transponders AFI,
the 2nd bit of the MASK is compared to the 2nd most
significant bit of the Transponders AFI and so on, up to
the 8th bit of the MASK, which is compared to the AFI. If
the 1st 8 bits of the MASK contain the value B00000000,
the result of the comparison of the 1st 8 bits of the MASK
specified in
the MASK LENGTH parameter.
to the AFI is forced to a Match result. If the
Transponders with data matching the MASK in the
command will move from the ROUND_ACTIVE or
ROUND_STANDBY or READY states to the
ROUND_ACTIVE state and commence participation in
the Arbitration process. Transponders whose data does
not match the MASK value sent in the command will
remain in the READY state or they will move to the
READY state if they are already in the ROUND_ACTIVE
or ROUND_STANDBY states.
MASK_LENGTH is less than 8 bits, then the number of
bits of the Transponder’s AFI compared to the MASK is
determined by the MASK_LENGTH parameter.
The 9th to the 136th bits of the MASK is compared to the
128 bit USER DATA in the Transponder – in other words,
bit 9 of the MASK is compared to the MSB of the USER
DATA and so on down to bit 136 of the MASK being
compared to the LSB of the USER DATA. The number of
bits of the USER DATA compared to the MASK is equal
to MASK_LENGTH – 8 if MASK_LENGTH > 8. If
MASK_LENGTH ≤ 8 no USER DATA bits will be
compared to the MASK.
Tags in the QUIET state will ignore the BEGIN_ROUND
command.
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