VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Datas heet
Multi-Gigabit Interconnect Chip
VSC7217
mary or redundant serial input as the data source for that channel. When RXP/RC is HIGH, the C channel serial
data source is PRXC. When LBENn(1:0)=10, the channel’s transmitter is looped back and becomes the serial
data source regardless of the state of RXP/Rn (see Table 4).
Table 4: Serial Data Source Selection
LBENn(1:0)
RXP/Rn
Serial Data Source
¹ 1 0
¹ 1 0
0
1
RRXn
PRXn
LBTXn
Loopback fromTransmitters
= 1 0
X
Signal Detection
Each channel’s primary and redundant PECL input buffers have an associated signal detect output,
PSDETn and RSDETn. All eight outputs are available for continuous monitoring of both the selected and non-
selected input. Each signal detect output is asserted HIGH when transitions are detected on the associated PECL
input and the signal amplitude exceeds 200 mV. A LOW indicates that either no transitions are detected or the
signal amplitude is below 100mV. The signal detect outputs are considered undefined when the signal ampli-
tude is in the 100mV to 200 mV range. The signal detect circuitry behaves like a re-triggerable one shot that is
triggered by signal transitions, and whose time-out interval ranges from 40 to 80 bit times. The transition den-
sity is not checked to ensure that it corresponds to a valid Fibre Channel data stream. The PSDETn and
RSDETn output timing is identical to the low-speed receiver outputs, as selected by RMODE(1:0) in Table 5.
Receiver Equalization
Incoming data on the PRX/RRX inputs typically contains a substantial amount of Inter Symbol Interfer-
ence (ISI) or deterministic jitter which reduces the ability of the receiver to recover data without errors. An
equalizer has been added to each of the receiver’s input buffers in order to compensate for this deterministic jit-
ter. This circuit has been designed to effectively reduce the ISI commonly found in copper cables or backplane
traces due to low frequencies traveling faster than high frequencies as a result of the skin effect. The equalizer
boosts high-frequency edge response in order to reduce the adverse effects of ISI.
Clock and Data Recovery
At the receiver, each channel contains an independent Clock Recovery Unit (CRU) that accepts the selected
serial input source, extracts the high-speed clock and retimes the data. Each CRU automatically locks on data
and if the data is not present, will automatically lock to the REFCLK. This maintains a very well-behaved
recovered clock (RCLKn/RCLKNn) which does not contain any slivers and will operate at a frequency of the
REFCLK reference ±200 ppm. The use of an external Lock-to-Reference pin is not needed.
The Clock Recovery Unit must perform bit synchronization which occurs when the CRU locks onto and
properly samples the incoming serial data as described in the previous paragraph. When the CRU is not locked
onto the serial data, the 10-bit data out of the decoder is invalid which results in numerous 8B/10B decoding
errors or disparity errors. When the link is disturbed (the cable is disconnected or the serial data source is
switched), the CRU will require a certain amount of time to lock onto data which is specified in the AC timing
specifications for “Data Acquisition Lock Time.”
G52325-0, Rev. 3.0
6/14/00
Ó VITESSE SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
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