VSC7212 Datasheet, PDF (7/34 Pages) Vitesse Semiconductor Corporation – Gigabit Interconnect Chip

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Preliminary Data Sheet
VSC7212
Gigabit Interconnect Chip
Receiver Functional Description
Serial Data Source
The receiver has both primary and redundant serial input ports, PRX and RRX, respectively, which consist
of differential PECL input buffers. It also has a control input, RXP/R, used to select either the primary or
redundant serial input as the data source. When RXP/R is HIGH, the serial data source is PRX. When
LBEN(1:0)=10, the transmitter is looped back and becomes the serial data source regardless of the state of
RXP/R (see Table 4).
Table 4: Serial Data Source Selection
LBEN(1:0)
≠10
≠10
=10
RXP/R
0
1
X
Serial Data Source
RRX
PRX
LBTX (Loopback from PTX/RTX)
Signal Detection
The primary and redundant PECL input buffers have an associated signal detect output, PSDET and
RSDET. Both outputs are available for continuous monitoring of 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 200mV. 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 amplitude is in the 100mV to
200mV 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 density is not checked to
make sure that it corresponds to a valid Fibre Channel data stream. The PSDET and RSDET 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 input typically contains a substantial amount of Inter Symbol Interference
(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 jitter. 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.
G52268-0, Rev 3.3
04/10/01
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