The HDMP-0482 design allows for
CDR placement at any location
with respect to the hard disk
slots. For example, if the BY-
PASS[0]- pin is floating and hard
disk slots A to G are connected to
PBC cells 1 to 7, respectively, the
CDR function will be performed
before entering the hard disk at
slot A. To obtain a CDR function
after slot G, BYPASS[1]- must be
floating and hard disk slots A to
G must be connected to PBC cells
2,3,4,5,6,7 and 0, respectively.
Table 1 shows all possible
connections.
For configurations where the CDR
is before slot A, a Data Valid
(FM_NODE[0]_DV) pin indicates
whether the incoming data on
FM_NODE[0]± is valid Fibre
Channel data. In addition, an
Amplitude Valid (FM_NODE[7]AV)
pin shows the status of the signal
at FM_NODE[7].
7
0
FM_NODE(7)_AV
AV
1
BYPASS1
2
BYPASS2
3
BYPASS3
4
BYPASS4
5
BYPASS5
6
BYPASS6
1
0
1
0
1
0
1
0
1
0
1
0
1
0
BYPASS7
1
0
0
1
FM_NODE[0]_DV
DV
CDR
MODE_VDD
BYPASS0
FSEL
REFCLK
RFCM
MODE_VDD
BYPASS0
Figure 1. Block Diagram of HDMP-0482.
HDMP-0482 Block Diagram
CDR
The Clock and Data Recovery
(CDR) block is responsible for
frequency and phase locking onto
the incoming serial data stream
and resampling the incoming
data based on the recovered
clock. An automatic locking
feature allows the CDR to lock
onto the input data stream
without external training con-
trols. It does this by continually
frequency locking onto the
106.25 MHz reference clock
(REFCLK) and then phase
locking onto the input data
stream. Once bit locked, the CDR
generates a high-speed sampling
clock. This clock is used to
sample or repeat the incoming
data to produce the CDR output.
The CDR jitter specifications
listed in this data sheet assume
an input that has been 8B/10B
encoded.
DV Output
The Data Valid (DV) block detects
if the incoming data on
FM_NODE[0]± is valid Fibre
Channel data. The DV checks for
sufficient K28.5+ characters (per
Fibre Channel framing rules) and
for run length violations (per 8B/
10B encoding) on the data
coming out of the CDR. The
FM_NODE[0]_DV output is
pulled low if a run length viola-
tion (RLV) occurs, or if there are
no commas detected (NCD) in a
sufficient time. It is pulled high if
no errors are found. A RLV error
is defined as any consecutive
sequence of 1s or 0s greater than
five in the serial data bit stream.
A NCD error indicates the
absence of a seven-bit pattern
(0011111) present in the positive
disparity comma (K28.5+)
character. A K28.5+ character
should occur at the beginning of
every Fibre Channel frame of
2148 bytes (or 21480 serial bits),
as well as many times within and
between frames. If this seven-bit
pattern is not found within a 2
15
bit (~31
µs)
interval, an NCD
error is generated.
2
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