ESE

SEMICONDUCTOR CORPORATION

VITESSE

SEMICONDUCTOR CORPORATION

Preliminary Data Sheet

VSC7212

Gigabit Interconnect Chip

Page 14

G52268-0, Rev 3.3

04/10/01

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

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

Internet: www.vitesse.com

Receiver State Machine

The VSC7212 contains a Loss of Synchronization State Machine (LSSM) which is responsible for

detecting and handling loss of bit and word clock synchronization in a controlled manner. There are three states

in the LSSM: LOSS_OF_SYNC, RESYNC and SYNC_ACQUIRED as shown in the state diagram of Figure 9.

The RESYNC state is entered when a 10-bit word has been received which contains the 7-bit “Comma” pattern

(e.g., a K28.5 IDLE character). After entering the RESYNC state, the VSC7212 will stay in it until a valid,

“non-Comma” transmission is received, then it transitions to the SYNC_ACQUIRED state indicating a normal

operating condition. The RESYNC state is re-entered if four consecutive “Commas” are received or if a single

“Comma” is received that changes the 10B character framing boundary. The LOSS_OF_SYNC state is entered

whenever four consecutive invalid transmissions have been detected or when the occurrences of invalid

transmission outnumber those of valid transmission by four. The relative occurrences of invalid vs. valid

transmissions are monitored with a simple up/down counter that increments when an invalid transmission is

detected and decrements otherwise. The LSSM transitions to the LOSS_OF_SYNC state when the counter

reaches four, and the counter is reset. A state diagram for the invalid transmission counter is shown in

Figure 10. The VSC7212 receiver will stay in the LOSS_OF_SYNC state until a valid “Comma” pattern is

detected. Note that the RESYNC state is entered whenever the 10B framing boundary is changed, and whenever

the Word Sync Sequence is received. When ENDEC is LOW, the LSSM logic is disabled.

Figure 9: State Diagram of the Loss of Synchronization State Machine

RESYNC

IDLE=1

ERR=1

KCH=1

Four Consecutive

Invalid Transmissions

Valid “Comma”

Valid “Non-Comma”

(K28.1, K28.5, K28.7)

or

Invalid minus Valid

Transmissions is > 4

LOSS_OF_SYNC

IDLE=0

ERR=1

KCH=1

Valid “Comma”

Invalid Transmission

SYNC_ACQUIRED

IDLE=X

ERR=0

KCH=X

IDLE=X

ERR=1

KCH=0

or

Four Consecutive “Commas”

or

Mis-Aligned “Comma”