TLK2501

1.5 TO 2.5 GBPS TRANSCEIVER

SLLS427D − AUGUST 2000 − REVISED JULY 2003

11

POST OFFICE BOX 655303

detailed description (continued)

loss of signal detection

The TLK2501 has a loss of signal detection circuit for conditions where the incoming signal no longer has a

sufficient voltage level to keep the clock recovery circuit in lock. The signal detection circuit is intended to be

an indication of gross signal error conditions, such as a detached cable or no signal being transmitted, and not

an indication of signal coding health. The TLK2501 reports this condition by asserting, the RX_DV/LOS, RX_ER

and RXD[0:15] all to a high state. As long as the signal is above 200 mV in differential magnitude, the LOS circuit

does not signal an error condition.

power down mode

When the ENABLE pin is deasserted low, the TLK2501 will go into a power down mode. In the power down

mode, the serial transmit pins (DOUTTXP, DOUTTXN), the receive data bus pins (RXD[0:15]), and RX_ER will

go into a high-impedance state. In the power-down mode the RX_DV/LOS pin acts as an output of the signal

detection circuit which remains active. If the signal detection circuit detects a valid differential signal amplitude

of >200 mV on each of the serial receive pins (DINRXP, DINRXN), RX_DV/LOS is driven high. If no signal of

sufficient amplitude is detected, the signal detection circuit will indicate a loss of signal by driving RX_DV/LOS

low. In the power-down condition, the signal detection circuit draws less than 5 mW.

synchronization and initialization

The TLK2501 has a synchronization-state machine which is responsible for handling link initialization and

synchronization. Upon power up or reset, the state machine enters the acquisition (ACQ) state and searches

for IDLE. Upon receiving three consecutive IDLEs or carrier extends, the state machine enters the

synchronization (SYNC) state. If, during the acquisition process, the state machine receives valid data or an

error propagation code, it immediately transitions to the SYNC state. The SYNC state is the state for normal

device transmission and reception. The initialization and synchronization state diagram is provided in Figure 6.

4 Consecutive Valid Code Words Received

Power-Up/Reset

Invalid Code

Word Received

ACQ

(Link Acquisition)

3 Invalid Code

Words Received

Loss of Link

Link in Question

1 Invalid Code

Word Received

CHECK

(Look for Valid Code)

Link Re-established

SYNC

(Normal Operation)

Link Established

3 Consecutive Valid IDLEs or Carrier Extends,

or

1 Valid Data or Error Propagation

Valid Code

Word Received

Figure 6. Initialization and Synchronization State Diagram