MOTOROLA
Chapter 3. Receiver
3-9
Data Alignment Configurations
3.5.1
Non-Aligned Mode (BSYNC = Low)
In non-aligned mode no attempt is made to align the incoming data stream. The bits are
simply accumulated into 10-bit code groups and forwarded. This mode should be used only
with backplane 10- or 5-bit data mode (TBIE = high, COMPAT = low), and with word
synchronization disabled (WSYNC1 = low and WSYNC0 = low).
3.5.2
Byte-Aligned Mode (BSYNC = High)
The remaining 4 receiver operating modes, shown in Table 3-4 align the incoming serial
data into 10-bit code groups. At power up, the receiver starts an alignment procedure,
searching for the 8-bit pattern defined by the 8B/10B COMMA codes. Synchronization
logic checks for the distinct sequence, ‘00111110xx’ and ‘11000001xx’ (ordered bit 0–7),
characteristic of the three valid COMMA code group patterns. The search is done on the
10-bit data in the receiver, and is, therefore, independent of the state of TBIE or COMPAT.
Alignment requires a minimum of four, error-free, received COMMA code groups to
ensure proper alignment and lock. Non-COMMA code groups may be interspersed with the
COMMA code groups. The disparity of the COMMA code groups is not important to
alignment and can be positive, negative, or any combination. The receiver begins to
forward received code groups once locked on an alignment.
If in the GMII or RGMII mode, alignment is acquired per the PCS state diagram as shown
in Figure 36-9 of the IEEE Std. 802.3 2002 specification [4].
Alignment remains locked until any one of three events occur that indicate loss of
alignment:
•
Alignment is lost when a misaligned COMMA sequence is detected. The MC92603
can be configured to automatically realign to a new COMMA sequence. This mode
is always enabled when in backplane byte mode or GMII mode (TBIE low) or when
both XMIT
_x_
K and TBIE are high. If automatic realignment is allowed then
alignment is lost (and immediately regained) when a misaligned COMMA sequence
is detected. A misaligned COMMA sequence is defined as four COMMA code
groups with a new alignment other than the current alignment. Non-COMMA code
groups can be dispersed between the four misaligned COMMAs; however, a
properly-aligned COMMA code group or a COMMA code group with yet another
alignment breaks the sequence. When alignment is lost due to misaligned
COMMAs, the receiver is automatically aligned to the new COMMA sequence and
data continues without interruption. Also, if realignment is allowed by the state of
XMIT
_x_
K when in TBI mode, the FIFOs are automatically realigned to keep all
IDLE code group output relative to RECV
_x_
RCLK_B (see Section 3.7.1.2, “TBI
Operation”). If word synchronization is enabled, any byte realignment will cause
loss of word synchronization (see “Section 3.5.3.1, “Word Synchronization
Method”).
Summary of Contents for MC92603
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