VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Datasheet

VSC7139

Quad Transceiver for

Gigabit Ethernet and Fibre Channel

G52196-0, Rev 3.3

Page 3

5/14/01

© VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012

Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

Serializer

The VSC7139 accepts TTL input data as a parallel 10 bit character on the Tx(0:9) bus which is latched into

the input register on the rising edge of either REF or TBCx. Three clocking modes are available and automati-

cally detected by the VSC7139. If TBCC is static and RFCM is HIGH, then all four Tx(0:9) busses are latched

on the rising edges of REF. If TBCC is static and RFCM is LOW, then REF is multiplied by 20 and the input

busses are latched on the rising edges of REF and at the midpoint between rising edges. If TBCC is toggling but

TBCB is static, then all four Tx(0:9) busses are latched on the rising edges of TBCC. If TBCB and TBCC are

both toggling then the rising edge of each TBCx latches the corresponding Tx(0:9) bus.

The active TBCC or TBCx inputs must be frequency-locked to REF. There is no specified phase relation-

ship. Prior to normal data transmission, LTCN must be asserted LOW so that the VSC7139 can lock to TBCx

which may result in corrupted data being transmitted. Once LTCN has been raised HIGH, the transmitters

remain locked to REF and can tolerate +2 bit times of drift in TBCx relative to REF.

The 10-bit parallel transmission character will be serialized and transmitted on the Tx PECL differential

outputs at the baud rate with bit Tx0 (bit a) transmitted first. User data should be encoded using 8B/10B or an

equivalent code. The mapping to 10B encoded bit nomenclature and transmission order is shown in Table 1,

along with the recognized comma pattern.

Table 1: Transmission Order and Mapping of a 10B Character

Clock Recovery

The VSC7139 accepts differential high speed serial input from the selected source (either the PECL Rx+/

Rx- pins or the internal Tx+/- data), extracts the clock and retimes the data. Equalizers are included in the

receiver to open the data eye and compensate for InterSymbol Interference (ISI) which may be present in the

incoming data. The serial bit stream should be encoded so as to provide DC balance and limited run length by

an 8B/10B encoding scheme. The digital Clock Recovery Unit (CRU) is completely monolithic and requires no

external components. For proper operation, the baud rate of the data stream to be recovered should be within

+200 ppm of ten times the REF frequency. For example, Gigabit Ethernet systems would use 125MHz oscilla-

tors with a +100ppm accuracy resulting in +200 ppm between VSC7139 pairs.

Deserializer

The recovered serial bit stream is converted into a 10-bit parallel output character. The VSC7139 provides

complementary TTL recovered clocks, RCx0 and RCx1, which are at one-twentieth of the serial baud rate (if

RCM=LOW) or one-tenth (if RCM=HIGH). The clocks are generated by dividing down the high-speed recov-

ered clock which is phase locked to the serial data. The serial data is retimed, deserialized and output on

Rx(0:9).

If serial input data is not present, or does not meet the required baud rate, the VSC7139 will continue to

produce a recovered clock so that downstream logic may continue to function. The RCx0/RCx1 output fre-

quency under these circumstances will differ from its expected frequency by no more than +1%.

Data Bit

Tx9

Tx8

Tx7

Tx6

Tx5

Tx4

Tx3

Tx2

Tx1

Tx0

10B Bit Position

j

h

g

f

i

e

d

c

b

a

Comma Character

x

x

x

1

1

1

1

1

0

0