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INITIALIZATION MODE

SYNCHRONIZATION MODE

SN65LV1023A-EP

SN65LV1224B-EP

SGLS358 – SEPTEMBER 2006

FUNCTIONAL DESCRIPTION (continued)

Initialization of both devices must occur before data transmission can commence. Initialization refers to

synchronization of the serializer and deserializer PLLs to local clocks.

begins locking to a local clock. For the serializer, the local clock is the transmit clock (TCLK) provided by an

external source. For the deserializer, a local clock must be applied to the REFCLK pin. The serializer outputs

remain in the high-impedance state, while the PLL locks to the TCLK.

The deserializer PLL must synchronize to the serializer in order to receive valid data. Synchronization can be

accomplished in one of two ways:

•

Rapid Synchronization: The serializer has the capability to send specific SYNC patterns consisting of six

ones and six zeros switching at the input clock rate. The transmission of SYNC patterns enables the

deserializer to lock to the serializer signal within a deterministic time frame. This transmission of SYNC

patterns is selected via the SYNC1 and SYNC2 inputs on the serializer. Upon receiving valid SYNC1 or

SYNC2 pulse (wider than 6 clock cycles), 1026 cycles of SYNC pattern are sent.

When the deserializer detects edge transitions at the LVDS input, it attempts to lock to the embedded clock

information. The deserializer LOCK output remains high while its PLL locks to the incoming data or SYNC

patterns present on the serial input. When the deserializer locks to the LVDS data, the LOCK output goes

low. When LOCK is low, the deserializer outputs represent incoming LVDS data. One approach is to tie the

deserializer LOCK output directly to SYNC1 or SYNC2.

•

Random-Lock Synchronization: The deserializer can attain lock to a data stream without requiring the

serializer to send special SYNC patterns. This allows the SN65LV1224B to operate in open-loop

applications. Equally important is the deserializer’s ability to support hot insertion into a running backplane.

In the open-loop or hot-insertion case, it is assumed the data stream is essentially random. Therefore,

because lock time varies due to data stream characteristics, the exact lock time cannot be predicted. The

primary constraint on the random lock time is the initial phase relation between the incoming data and the

REFCLK when the deserializer powers up.

The data contained in the data stream can also affect lock time. If a specific pattern is repetitive, the deserializer

could enter false lock—falsely recognizing the data pattern as the start/stop bits. This is referred to as repetitive

multitransition (RMT); see Figure 2 for RMT examples. This occurs when more than one low-high transition

takes place per clock cycle over multiple cycles. In the worst case, the deserializer could become locked to the

data pattern rather than the clock. Circuitry within the deserializer can detect that the possibility of false lock

exists. Upon detection, the circuitry prevents the LOCK output from becoming active until the potential false lock

pattern changes. Notice that the RMT pattern only affects the deserializer lock time, and once the deserializer is

in lock, the RMT pattern does not affect the deserializer state as long as the same data boundary happens each

cycle. The deserializer does not go into lock until it finds a unique four consecutive cycles of data boundary

(stop/start bits) at the same position.

The deserializer stays in lock until it cannot detect the same data boundary (stop/start bits) for four consecutive

cycles. Then the deserializer goes out of lock and hunts for the new data boundary (stop/start bits). In the event

of loss of synchronization, the LOCK pin output goes high and the outputs (including RCLK) enter a

high-impedance state. The user’s system should monitor the LOCK pin in order to detect a loss of

synchronization. Upon detection of loss of lock, sending sync patterns for resynchronization is desirable if

reestablishing lock within a specific time is critical. However, the deserializer can lock to random data as

previously noted.

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