|Category||Interface and Interconnect => LVDS (Low Voltage Differential Signaling) => Bus LVDS Serializer / Deserializer Devices|
|Description||DS92LV1212 - 16 MHZ - 40 MHZ 10-Bit Bus LVDS Random Lock Deserializer With Embedded Clock Recovery Not Recommended For Designs , Package: SSOP-EIAJ, Pin Nb=28|
|Company||National Semiconductor Corporation|
|Datasheet||Download DS92LV1212TMSAX datasheet
|Cross ref.||Similar parts: DS92LV1021A, SN65LV1021, DS92LV1224, SN65LV1224B, SN65LV1224B-EP|
|DS92LV1212 16-40 MHz 10-Bit Bus LVDS Random Lock Deserializer with Embedded Clock Recovery
The is an upgrade of the DS92LV1210. It maintains all of the features of the DS92LV1210 with the additional capability of locking to the incoming data stream without the need of SYNC patterns. This makes the DS92LV1212 useful in applications where the Deserializer must be operated "open-loop" without a feedback path from the Deserializer to the Serializer. The DS92LV1212 is designed to be used with the DS92LV1021 Bus LVDS Serializer. The DS92LV1212 receives a Bus LVDS serial data stream and transforms it into a 10-bit wide parallel data bus and separate clock. The reduced cable, PCB trace count and connector size saves cost and makes PCB layout easier. Clock-to-data and data-to-data skews are eliminated since one input receives both clock and data bits serially. The powerdown pin is used to save power by reducing the supply current when the device is not in use. The Deserializer will establish lock to a synchronization pattern within specified lock times but it can also lock to a data stream without SYNC patterns.Features
n Clock recovery without SYNC patterns-random lock n Guaranteed transition every data transfer cycle n Chipset (Tx + Rx) power consumption < 300mW (typ) 40MHz n Single differential pair eliminates multi-channel skew n 400 Mbps serial Bus LVDS bandwidth (at 40 MHz clock) n 10-bit parallel interface for 1 byte data plus 2 control bits or UTOPIA I Interface n Synchronization mode and LOCK indicator n Flow-through pinout for easy PCB layout n High impedance on receiver inputs when power is off n Programmable edge trigger on clock n Footprint compatible with DS92LV1210 n Small 28-lead SSOP package-MSATRI-STATE is a registered trademark of National Semiconductor Corporation.
The a 10-bit Deserializer chip designed to receive data over a heavily loaded differential backplanes at clock speeds from 16 MHz to 40 MHz. It may also be used to receive data over Unshielded Twisted Pair (UTP) cable. The chip has three active states of operation: Initialization, Data Transfer, and Resynchronization; and two passive states: Powerdown and TRI-STATE The following sections describe each operation and passive state.
formation. When the Deserializer locks to the Bus LVDS clock, the LOCK output will go low. When LOCK is low the Deserializer outputs represent incoming Bus LVDS data.
Serialized data and clock bits (10+2 bits) are received at 12 times the TCLK frequency. For example, if TCLK is 40 MHz, the serial rate = 480 Mega bits per second. Since only 10 bits are from input data, the serial "payload" rate is 10 times the TCLK frequency. For instance, if TCLK = 40 MHz, the payload data rate = 400 Mbps. TCLK is provided by the data source and must be in the range 16 MHz to 40 MHz nominal. The LOCK pin on the Deserializer is driven low when it is synchronized with the Serializer. The Deserializer locks to the embedded clock and uses it to recover the serialized data. ROUT data is valid when LOCK is low. Otherwise ROUT0ROUT9 is invalid. RCLK pin is the reference to data on the ROUT0-ROUT9 pins. The polarity of the RCLK edge is controlled by the RCLK_R/F input. ROUT(0-9), LOCK and RCLK outputs will drive a minimum of three CMOS input gates (15 pF load) with 40 MHz clock.
Before data can be transferred the Deserializer must be initialized. The Deserializer should be powered up with the PWRDN pin held low. After VCC stabilizes the PWRDN pin can be forced high. The Deserializer is ready to lock to the incoming data stream. Step 1: When VCC is applied to the Deserializer, the respective outputs are held in TRI-STATE and internal circuitry is disabled by on-chip power-on circuitry. When VCC reaches VCC OK (2.5V) the PLL is ready to lock to incoming data or synchronization patterns. The local clock is applied to the REFCLK pin. The Deserializer LOCK output will remain high while its PLL is locking to the incoming data or to SYNC patterns on the input. Step 2: The Deserializer PLL must synchronize to the Serializer to complete the initialization. The Deserializer will lock to non-repetitive data patterns, however, the transmission of SYNC patterns to the Deserializer enables the Deserializer to lock to the Serializer signal within a specified time. Control of the Serializer SYNC1/2 pins is left to the user. A feedback loop between the LOCK pin is one recommendation. Another option is that one or both of the Serializer SYNC inputs are asserted for at least 1024 cycles of TCLK to initiate transmission of SYNC patterns. The Serializer will continue to send SYNC patterns after the minimum 1024 if either of the SYNC inputs remain high. When the Deserializer detects edge transitions at the Bus LVDS input it will attempt to lock to the embedded clock in-
The Deserializer LOCK pin driven low indicates that the Deserializer PLL is locked to the embedded clock edge. If the Deserializer loses lock, the LOCK output will go high and the outputs (including RCLK) will be TRI-STATE. The LOCK pin must be monitored by the system to detect a loss of synchronization. The system can arrange to pulse the Serializer or SYNC2 pin to resynchronize. There are multiple approaches possible. One recommendation is to provide a feedback loop using the LOCK pin itself to control the sync request of the Serializer SYNC2). A minimum of 1024 sync patterns are needed to resynchronize. Dual SYNC pins are provided for multiple control in a multi-drop application.
The initialization and resynchronization methods described in their respective sections are the fastest ways to establish the link between the Serializer and Deserializer, however, the DS92LV1212 can attain lock to a data stream without requiring special SYNC patterns to be sent by the Serializer. This allows the to be used in applications where the Deserializer must operate "open-loop" and supports hot insertion into a running backplane. Because the data stream is essentially random the time for the DS92LV1212 to attain lock is variable and cannot be predicted. The primary constraint on the "random" lock time is the initial phase relation when the Deserializer is powered up. The data contained in the data stream can also affect lock time. Typical lock times for random data have a mean of 570us and a max If a specific pattern is repetitive the Deserializer could be misled into a "false lock" - falsely recognizing the data pattern as the clocking bits. We refer to such a pattern as a repetitive multi-transition, RMT. This is when there is more than one Low-High transition in a single clock cycle. This occurs when any bit, except DIN 9, is held at a low state and the adjacent bit is held high creating a 0-1 transition. In the worst case the Deserializer could become locked to the data pattern rather than the clock. Circuitry within the DS92LV1212 can detect that the possibility of "false lock" exists (by detecting that there is more than 1 potential position for clocking bits) and will prevent the LOCK* output from becoming active until the potential "false lock" pattern changes. It is expected that the data will eventually change causing the Deserializer to lose lock to the data pattern and continue searching for the clock bits in the serial data stream. A graphical representation of a few cases of RMT is shown below. Please note that RMT applies to bits DIN0-DIN8.
The Powerdown state is a low power sleep mode that can be used to reduce power when there is no data to be transferred. Powerdown is entered when PWRDN and REN are driven low on the Deserializer. In Powerdown, the PLL is stopped and the outputs go into TRI-STATE, disabling load current and also reducing supply current to the milliamp range. To exit Powerdown, PWRDN is driven high. Both the Serializer and Deserializer must re-initialize and resynchronize before data can be transferred. Initialization of the Serializer takes 1024 TCLK cycles. The Deserializer will initialize and assert LOCK high until it is locked to the Bus LVDS clock.
For the Deserializer, TRI-STATE is entered when the REN pin is driven low. This will TRI-STATE the receiver output pins (ROUT0ROUT9), LOCK and RCLK.
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