Datasheet

TLK2541
www.ti.com SLLS779B –JANUARY 2008– REVISED APRIL 2008
Table 5. Receive Status Signals
RXD[16] RXD[17] DECODED 20 BIT OUTPUT FULL RATE WITH 8B/10B CODING
0 0 Valid data on RXD[0:7], Valid data RXD[8:15]
0 1 Valid data on RXD[0:7], K code on RXD[8:15]
1 0 K code on RXD[0:7], Valid data on RXD[8:15]
1 1 K code on RXD[0:7], K code on RXD[8:15]
RXD[16] DECODED 20 BIT OUTPUT HALF RATE WITH 8B/10B CODING
0 Valid data on RXD[0:7]
1 K code on RXD[0:7]
Table 6. Valid K Characters
RECEIVE DATA BUS
K CHARACTER
(RXD[0:7]) OR (RXD[8:15])
K28.0 000 11100
K28.1
(1)
001 11100
K28.2 010 111000
K28.3 011 111000
K28.4 100 11100
K28.5
(1)
101 11100
K28.6 110 111001
K28.7
(1)
111 11100
K23.7 111 101111
K27.7 111 110111
K29.7 111 111011
K30.7 111 111101
(1) Should only be present on RXD[7–0] when in running disparity < 0.
Lock to Reference
When the LCKREFN pin is asserted (active low), the tracking circuitry on the receiver Clock/Data Recovery
(CDR) circuit is disabled, and the recovered byte clock becomes a buffered version of REFCLK. If there is not a
valid serial data stream while the receiver is attempting to lock onto and track a serial data stream, then it is
possible for the recovered byte clock to drift to a frequency above or below the desired data rate by as much as
2000 ppm depending on noise components of the invalid input serial data stream. The assertion of LCKREFN,
while there is no valid incoming serial data, would ensure that the recovered byte clock does not drift away from
REFCLK. The use of LCKREFN is not required to help the receiver lock onto incoming serial data, and the use of
LCKREFN does not speed the process of locking onto data once LCKREFN is released.
Power Down Mode
When the reference clock (REFCLK) is held static, the TLK2541 goes into power-down mode. In power-down
mode, the serial transmit pins (TXN and TXP) , and the receive data bus pins (RXD[0:19]) go into a
high-impedance state. When the reference clock begins to toggle at a rate approaching its minimum
recommended operating frequency then the TLK2541 will go through its power-on reset procedure.
PRBS Verification
The TLK2541 also has a built-in BERT function in the receiver side that is enabled by the PRBSEN. It can check
for errors and report the errors by forcing the PRBSPASS terminal low.
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