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8

PLL Circuitry

The CKREF input signal is used to provide a reference to the

PLL. The PLL will generate internal timing signals capable of

transferring data at 26 times the incoming CKREF signal. The

output of the PLL is a Bit Clock that is used to serialize the data.

The bit clock is also sent source synchronously with the serial

data stream.

There are two ways to disable the PLL. The PLL can be dis-

abled by entering the Mode 0 state (S1 = S2 = 0). The PLL will

disable immediately upon detecting a LOW on both the S1 and

S2 signals. When any of the other modes are entered by assert-

ing either S1 or S2 HIGH and by providing a CKREF signal the

PLL will power-up and goes through a lock sequence. One must

wait the specified number of clock cycles prior to capturing valid

data into the parallel port. When the

PSerDes chipset transitions

from a power down state (S1, S2 = 0, 0) to a powered state

(example S1, S2 = 1, 1), CKP on the deserializer will transition

LOW for a short duration, and will return HIGH. Following this,

the signal level of the deserializer at CKP will correspond to the

serializer signal levels.

An alternate way of powering down the PLL is by stopping the

CKREF signal either HIGH or LOW. Internal circuitry detects the

lack of transitions and shuts the PLL and serial I/O down. Inter-

nal references will not however be disabled allowing for the PLL

to power-up and re-lock in a lesser number of clock cycles than

when exiting Mode 0. When a transition is seen on the CKREF

signal the PLL will once again be reactivated.

FIGURE 8. Simplified Block Diagram for Unidirectional Serializer and Deserializer

Figure 8 shows the basic operation diagram when a pair of Ser-

Des is configured in an unidirectional operation mode.

Master Operation: The device will... (Please refer to Figure 8)

1. Be configured as a serializer at power-up based on the value

of the DIRI signal.

2. Accept CKREF_M word clock and generate a bit clock with

embedded word boundary. This bit clock will be sent to the

slave device through the CKSO port.

3. Receive parallel data on the rising edge of STROBE_M.

4. Generate and transmit serialized data on the DS signals

which is source synchronous with CKSO.

5. Generate an embedded word clock for each strobe signal.

Slave Operation: The device will...

1. Be configured as a deserializer at power-up based on the

value of the DIRI signal.

2. Accept an embedded word boundary bit clock on CKSI.

3. Deserialize the DS Data stream using the CKSI input clock.

4. Write parallel data onto the DP_S port and generate the

CKP_S. CKP_S will only be generated when a valid data

word occurs.