S2070 AMCC (Applied Micro Circuits Corp), S2070 Datasheet - Page 4

• Manufacturer Part Number: S2070
• Description: Fibre Channel Transceiver
• Manufacturer: AMCC (Applied Micro Circuits Corp)

4
RECEIVER DESCRIPTION
Whenever a signal is present, the receiver attempts
to recover the serial clock from the received data
stream. The S2070 searches the serial bit stream for
the occurrence of a positive polarity COMMA sync
pattern (0011111xxx positive running disparity) to
perform word synchronization. Once synchronization
on both bit and word boundaries is achieved, the
receiver provides the decoded data on its parallel
outputs.
Clock Recovery Function
Clock recovery is performed on the input data
stream. A simple state machine in the clock recovery
macro decides whether to acquire lock from the se-
rial data input or from the reference clock. The deci-
sion is based upon the frequency and run length of
the input serial data.
The lock to reference frequency criteria ensure that
the S2070 will respond to variations in the serial data
input frequency (as compared to the reference fre-
quency). The new lock state is dependent upon the
current lock state, as shown in Table 3. The run-
length criteria ensure that the S2070 will respond ap-
Table 3. Lock to Reference Frequency Criteria
S2070
C
r u
U
L
e r
n
S
S
S
S
S
o
o l
a t
a t
a t
a t
a t
t n
k c
k c
e t
e t
e t
e t
e t
e
L
e
d
o
d
c
k
P
4
2
L
8
4
<
8
>
<
4
>
L
v (
v (
v (
v (
v (
4
o t
7
2
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3
F
. s
. s
. s
. s
. s
8
3
4
6
e r
8
7
2
4
3
6
T
T
T
T
T
q
3
6
B
B
B
B
B
p
p
p
p
u
2
6
p
p
p
p
C
C
C
C
C
e
m
p
m
m
p
m
)
)
)
n
)
)
p
p
c
m
m
y
N
U
U
e
w
n
n
U
U
d
d
L
L
L
n
n
t e
t e
o
o
o
o l
o l
FIBRE CHANNEL/GIGABIT ETHERNET TRANSCEIVER
k c
r e
k c
r e
c
k c
k c
k
m
m
e
e
e
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d
d
S
n i
n i
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d
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d
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e t
propriately and quickly to a loss of signal. The run-
length checker flags a condition of consecutive ones
or zeros across 12 parallel words. Thus, 119 or less
consecutive ones or zeros does not cause signal loss,
129 or more causes signal loss, and 120 – 128 may
or may not, depending on how the data aligns across
byte boundaries. If both the off-frequency detect test
and the run-length test is satisfied, the CRU will at-
tempt to lock to the incoming data.
In any transfer of PLL control between the serial
data and the reference clock, the RBC0 and RBC1
remain phase continuous and glitch free, assuring
the integrity of downstream clocking.
Reference Clock Input
The reference clock must be provided from a low
jitter clock source. The frequency of the received
data stream must be within 200 ppm of the reference
clock to ensure reliable locking of the receiver PLL.
A single reference clock is provided to both the
transmit and receive PLLs.
Data Output
The S2070 provides either framed or unframed par-
allel output data, determined by the state of
EN_CDET. With EN_CDET held ACTIVE, the S2070
will detect and align to the 8B/10B COMMA
codeword anywhere in the data stream. When
EN_CDET is INACTIVE, no attempt is made to syn-
chronize on any particular incoming character.
Upon change of state of the EN_CDET input, the
COM_DET output response will be delayed by a
maximum of 3 byte times.
The COM_DET output signal is ACTIVE whenever
EN_CDET is active and the COMMA control charac-
ter is present on the RX[0:9] parallel data outputs.
The COM_DET output signal will be INACTIVE at all
other times.
June 14, 2000 / Revision F