MOTOROLA
Chapter 3. Receiver
3-11
Data Alignment Configurations
The 4/1 IDLE sequence is defined as four consecutive IDLE code groups followed by a
non-IDLE code group. The disparity-based IDLE sequence is 16 consecutive IDLE code
groups with improper disparity on the second and third IDLE code group in the sequence.
The disparity-based IDLE sequence is described further in Section 2.4.1, “Transmitting
Uncoded Data—8-/4-Bit Modes.” Optionally the special control character K28.3 (/A/) may
be used as a word synchronization event.
Word synchronization events must be generated at all concerned transmitters
simultaneously in order for synchronization to be achieved. Word synchronization events
must be received at all concerned receivers within 40 bit-times of each other.
Word synchronization events are used to establish a relationship between the received bytes
in each of the receivers. The bytes of a word are matched and presented simultaneously at
the receiver interface. Once synchronization is achieved the receiver tol6 bit-times
of drift between receivers. If drift e6 bit-times the receiver will continue to operate.
However, the received bytes will no longer be synchronized properly because the receiver
remains locked on the initially established synchronization. Word synchronization remains
locked until one of three events occur that indicate loss of synchronization.
•
Word synchronization lock is lost when one or more of the receivers lose or change
byte alignment. Byte alignment loss is described in Section 3.5.2, “Byte-Aligned
Mode (BSYNC = High).”
•
Lock is also lost when overrun/underrun is detected on one or more of the receivers,
see Section 3.6.2, “Reference Clock Timing Mode (RCCE = Low),” for more about
overrun/underrun.
•
Finally, both byte and word synchronization are lost when explicitly invalidated by
asserting XCVR_x_DISABLE high. Word synchronization lock is lost when
explicitly invalidated by asserting DROP_SYNC and XCVR_x_DISABLE high for
at least two clocks (see Section 3.5.2, “Byte-Aligned Mode (BSYNC = High),” for
details on performing drop sync).
When word synchronization is lost it must be re-established before data flow through the
receiver resumes.
The receiver interface is disabled during initial word alignment. No data is produced at its
outputs until word alignment is achieved and a word synchronization event has been
detected. When establishing word synchronization, or when word synchronization is lost,
‘not word sync’ error is reported as described in Section 3.8.1, “Byte Mode (Uncoded
Data).”
Word synchronization is possible in byte interface mode and TBI mode. However, word
synchronization may be dependent on the detection of simultaneously transmitted word
synchronization events that contain Idle characters. Therefore, if operating in TBI mode,
either the Idle character must be a supported member of the code set or the ‘A’ character
alignment must be used.
Summary of Contents for MC92603
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