TLK2541 Datasheet, PDF(14/26 Page) Texas Instruments

◁

TLK2541

SLLS779B â JANUARY 2008 â REVISED APRIL 2008...................................................................................................................................................... www.ti.com

PRBS Generator

The TLK2541 has a built-in 27-1 PRBS (pseudo random bit stream) function. When the PRBSEN terminal is

forced high, the PRBS test is enabled. A PRBS is generated and fed into the 10-bit parallel-to-serial converter

input register. Data from the normal input source is ignored during the PRBS mode. The PRBS pattern is then

fed through the transmit circuitry as if it were normal data and sent out to the transmitter. The output can be sent

to a BERT (bit error rate tester), the receiver of another TLK2541, or looped back to the receive input. Since the

PRBS is not really random but a predetermined sequence of ones and zeroes, the data can be captured and

checked for errors by a BERT.

Parallel-to-Serial

The parallel-to-serial shift register takes in the 20-bit wide data word multiplexed from the two parallel 8-bit/10-bit

encoders and converts it to a serial stream. The shift register is clocked on both the rising and falling edge of the

internally generated bit clock, which is 10 times the REFCLK input frequency. The LSB (TXD[0]) is transmitted

first.

High-Speed Data Output

The high-speed data output driver consists of a voltage mode logic (VML) differential pair optimized for a 50-â¦

impedance environment. The magnitude of the differential pair signal swing is compatible with pseudo emitter

coupled logic (PECL) levels when ac-coupled. The line can be directly-coupled or ac-coupled. See Figure 11 and

Figure 12 for termination details. The outputs also provide preemphasis to compensate for ac loss when driving a

cable or PCB backplane trace over a long distance (see Figure 7). The level of pre-emphasis is controlled by

PRE as shown in Table 4.

Table 4. Programmable Pre-emphasis

PRE

PRE-EMPHASIS LEVEL(%)

VOD(P), VOD(D) (1)

20%

Figure 7. Output Voltage Under Pre-emphasis

(|VTXPâVTXN|)

(1) VOD(p) : Voltage swing when there is a transition in the data

stream

VOD(d): Voltage swing when there is no transition in the data

stream.

RECEIVE INTERFACE

The receiver portion of the TLK2541 accepts 8-bit/10-bit encoded differential serial data. The interpolator and

clock recovery circuit locks to the data stream and extract the bit rate clock. This recovered clock is used to

retime the input data stream. The recovered clock is divided down to output a receive word clock that is output

on RX_CLK. The parallel data is presented on the parallel output bus according to four modes of operation. The

TLK2541 can operate as a 10 bit SERDES at 10 times the rate of REFCLK or as a 20 bit SERDES at 20 times

the rate of REFCLK. At either rate, the data may be deserialized, byte aligned and output exactly as it is

captured from the serial inputs or it may be decoded into data bytes by way on an integrated 8B/10B decoder.

Receive Data Bus

At full data rate, the receiver portion locks to an incoming serial data stream and deserializes the data into 20-bit

wide data words and outputs them on RXD[0:19] along with the RX_CLK. RX_CLK is aligned with the rising edge

in the center of the output data word. The first data bit received is output on RXD[0]. If the 8B/10B decoder is

enabled, the data is output as 16 bits of data plus two bits of status. The lower order byte is output on RXD[0:7]

and the higher order byte is output on RXD[8:15]. Bit RXD[16] indicates whether the lower order byte was

decoded as a Dx.y data word or a Kx.y control word. Bit RXD[17] indicates whether the higher order byte was

decoded as a Dx.y data word or a Kx.y control word. Bits RXD[18] and RTXD[19] are high impedance.

At half data rate, the receiver portion locks to an incoming serial data stream and deserializes the data into 10-bit

wide data words and outputs them on RXD[0:9] along with the RX_CLK. RX_CLK is aligned with the rising edge

Submit Documentation Feedback

Product Folder Link(s) :TLK2541

▷