SLRC400 Datasheet, PDF (101/130 Pages) NXP Semiconductors – I·CODE Reader IC

Philips Semiconductors
I•CODE Reader IC
Product Specification Rev. 2.0 November 2001
SL RC400
16.4.2.3 Collision Detection
If more than one label is within the RF-field during the label selection phase, they will respond
simultaneously. The SL RC400 supports the algorithm defined in ISO 15693 as well as the I•CODE1 anti-
collision algorithm to resolve data-collisions of label serial numbers by doing the so-called anti-collision
procedure. The basis for this is the ability to detect bit-collisions.
Bit-collision detection is supported by the used bit-coding scheme, namely the Manchester-coding. If in the
first and second half-bit of a bit a sub-carrier modulation is detected, instead of forwarding a 1 or a 0 a bit
collision will be signalled. To distinguish a 1 or 0-bit from a bit-collision, the SL RC400 uses the setting of
CollLevel. If the amplitude of the half-bit with smaller amplitude is larger than defined by CollLevel, the
SL RC400 indicates a bit-collision.
If a bit-collision is detected, the error flag CollErr is set.
Independent from the detected collision the receiver continues receiving the incoming data stream. In case of
a bit-collision, the decoder forwards 1 at the collision position.
Note: As an exception, if bit ZeroAfterColl is set, all bits received after the first bit-collision are forced to zero,
regardless whether a bit-collision or an unequivocal state has been detected. This feature eases for the
software to carry out the anti-collision procedure defined in ISO 15693.
When the first bit collision in a frame is detected, the bit position of this collision is stored in the CollPos
Register.
The collision position follows the table below:
Collision in Bit
SOF
LSBit of LSByte
…
MSBit of LSByte
LSBit of second Byte
…
MSBit of second Byte
LSBit of third Byte
…
Value of CollPos
0
1
…
8
9
…
16
17
…
Table 16-2: Returned Values for Bit Collision Positions
If a collision is detected in the SOF a frame error is reported and no data is forwarded to the FIFO buffer. In
this case the receiver continues to monitor the incoming signal and generates the correct notifications to the
µ-Processor when the ending of the faulty input stream is detected. This helps the µ-Processor to determine
the time when it is allowed next to send anything to the label.
101
Preliminary