18
DS90C124
,
DS90C241
SNLS209M –NOVEMBER 2005–REVISED JANUARY 2017
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Feature Description (continued)
serializer block is now ready to send data patterns. The deserializer output remains in TRI-STATE while its
PLL locks to the embedded clock information in serial data stream. Also, the deserializer LOCK output
remains low until its PLL locks to incoming data and sync-pattern on the RIN± pins.
2. The deserializer PLL acquires lock to a data stream without requiring the serializer to send special patterns.
The serializer that is generating the stream to the deserializer automatically sends random (non-repetitive)
data patterns during this step of the Initialization State. The deserializer locks onto the embedded clock
within the specified amount of time. An embedded clock and data recovery (CDR) circuit locks to the
incoming bit stream to recover the high-speed receive bit clock and re-time incoming data. The CDR circuit
expects a coded input bit stream. In order for the deserializer to lock to a random data stream from the
serializer, it performs a series of operations to identify the rising clock edge and validates data integrity, then
locks to it. Because this locking procedure is independent on the data pattern, total random locking duration
may vary. At the point when the CDR of the deserializer locks to the embedded clock, the LOCK pin goes
high and valid RCLK/data appears on the outputs. Note that the LOCK signal is synchronous to valid data
appearing on the outputs. The deserializer’s LOCK pin is a convenient way to ensure data integrity is
achieved on receiver side.
8.3.2 Data Transfer
After serializer lock is established, the inputs DIN0 to DIN23 may be used to input data to the serializer. Data is
clocked into the serializer by the TCLK input. The edge of TCLK used to strobe the data is selectable through the
TRFB pin. TRFB high selects the rising edge for clocking data and low selects the falling edge. The serializer
outputs (DOUT±) are intended to drive point-to-point connections as shown in Figure 19.
CLK1, CLK0, DCA, DCB are four overhead bits transmitted along the single LVDS serial data stream. The CLK1
bit is always high and the CLK0 bit is always low. The CLK1 and CLK0 bits function as the embedded clock bits
in the serial stream. DCB functions as the DC Balance control bit. It does not require any precoding of data on
transmit side. The DC Balance bit is used to minimize the short and long-term DC bias on the signal lines. This
bit operates by selectively sending the data either unmodified or inverted. The DCA bit is used to validate data
integrity in the embedded data stream. Both DCA and DCB coding schemes are integrated and automatically
performed within serializer and deserializer.
Serialized data and clock or control bits (24 +4 bits) are transmitted from the serial data output (DOUT±) at 28
times the TCLK frequency. For example, if TCLK is 35 MHz, the serial rate is 35 × 28 = 980 Mega bits per
second. Because only 24 bits are from input data, the serial payload rate is 24 times the TCLK frequency. For
example, if TCLK = 35 MHz, the payload data rate is 35 × 24 = 840 Mbps. TCLK is provided by the data source
and must be in the range of 5 MHz to 35 MHz nominal. The serializer outputs (DOUT±) can drive a point-to-point
connection. The outputs transmit data when the enable pin (DEN) is high, TPWDNB is high. The DEN pin may
be used to TRI-STATE the outputs when driven low.
When the deserializer channel attains lock to the input from a serializer, it drives its LOCK pin high and
synchronously delivers valid data and recovered clock on the output. The deserializer locks onto the embedded
clock, uses it to generate multiple internal data strobes, and then drives the recovered clock to the RCLK pin.
The recovered clock (RCLK output pin) is synchronous to the data on the ROUT[23:0] pins. While LOCK is high,
data on ROUT[23:0] is valid. Otherwise, ROUT[23:0] is invalid. The polarity of the RCLK edge is controlled by the
RRFB input. ROUT[23:0], LOCK, and RCLK outputs each drive a maximum of 8-pF load with 35-MHz clock.
REN controls TRI-STATE for ROUTn and the RCLK pin on the deserializer.
8.3.3 Resynchronization
If the deserializer loses lock, it automatically tries to re-establish lock. For example, if the embedded clock edge
is not detected one time in succession, the PLL loses lock and the LOCK pin is driven low. The deserializer then
enters the operating mode where it tries to lock to a random data stream. It looks for the embedded clock edge,
identifies it and then proceeds through the locking process. The logic state of the LOCK signal indicates whether
the data on ROUT is valid; when it is high, the data is valid. The system must monitor the LOCK pin to determine
whether data on the ROUT is valid.