HDMP-1012 datasheet(7/42 Pages) HP

7 / 42 page

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maintain frequency and phase

lock. The type of fill frames sent

(FF0 or FF1) is determined by the

FF input. In a duplex system, FF

is normally connected to the Rx’s

STAT1 pin.

The C-Field Encoder, based on

the inputs at DAV*, CAV*,

FLAGSEL, and FLAG, supplies

four encoded bits to the frame

mux. This encoded data contains

the master transition (which the

receiver uses for frequency

locking), as well as information

regarding the data type: control,

data, or fill frame. In order for the

FLAG bit to be used as an

additional data bit, FLAGSEL

must be set high for both the Tx

and the Rx.

D-Field Encoder

The D-Field Encoder provides the

remaining parallel word data to

the frame mux. Based on control

signals from the Control Logic,

the D-Field Encoder either

outputs the parallel information at

its data inputs (D0..D19) or the

designated Fill Frame. RST*,

when set low, resets the internal

chip registers.

Frame Mux

The Frame Mux accepts the

output from the C-Field and D-

Field Encoders. The four control

bits are attached to the data bits,

either 16 or 20 data bits based on

the M20SEL input. This parallel

information, now either 20 or 24

bits wide, is multiplexed to a

serial line based on the internal

high speed serial clock.

SIGN

The sign circuitry determines the

cumulative sign of the outgoing

data frame, containing the data

and control bits. This is used by

the accumulator/inverter to

maintain DC balance for the

transmission line.

Accumulator/Invert

The Accumulator/Invert block is

responsible for maintaining the

DC balance of the serial line. It

determines, based on history and

the sign of the current data frame,

whether or not the current frame

should be inverted to bring the

line closer to the desired 50%

duty cycle. INV is set high when

the data frame is inverted.

Output Select

In normal operation, the serial

data stream is placed at DOUT.

By asserting LOOPEN, the user

may also direct the serial data

stream to LOUT, which may be

used for loopback testing. When

LOOPEN is not asserted, LOUT is

disabled to reduce power

consumption.

HDMP-1012 Datasheet(PDF) 7 Page - Agilent(Hewlett-Packard)

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