DS90C124_13 Datasheet, PDF (17/31 Pages) Texas Instruments – 5-MHz to 35-MHz DC-Balanced 24-Bit FPD-Link II Serializer and Deserializer

DS90C124, DS90C241
www.ti.com
SNLS209L – NOVEMBER 2005 – REVISED APRIL 2013
Step 1: When V_CC is applied to both Serializer and/or Deserializer, the respective outputs are held in TRI-STATE
and internal circuitry is disabled by on-chip power-on circuitry. When V_CC reaches V_CC OK (2.2V) the PLL in
Serializer begins locking to a clock input. For the Serializer, the local clock is the transmit clock, TCLK. The
Serializer outputs are held in TRI-STATE while the PLL locks to the TCLK. After locking to TCLK, the Serializer
block is now ready to send data patterns. The Deserializer output will remain in TRI-STATE while its PLL locks to
the embedded clock information in serial data stream. Also, the Deserializer LOCK output will remain low until its
PLL locks to incoming data and sync-pattern on the RIN± pins.
Step 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 will automatically send random (non-
repetitive) data patterns during this step of the Initialization State. The Deserializer will lock onto 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 Deserializer’s CDR 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.
DATA TRANSFER
After Serializer lock is established, the inputs DIN0–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 via 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 20.
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 pre-coding 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/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 x 28 = 980 Mega bits per second.
Since only 24 bits are from input data, the serial “payload” rate is 24 times the TCLK frequency. For instance, if
TCLK = 35 MHz, the payload data rate is 35 x 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(0-23), LOCK and RCLK outputs will each drive a maximum of 8 pF load with a 35 MHz clock.
REN controls TRI-STATE for ROUTn and the RCLK pin on the Deserializer.
RESYNCHRONIZATION
If the Deserializer loses lock, it will automatically try 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.
Copyright © 2005–2013, Texas Instruments Incorporated
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