LMH0046

SNLS222F – APRIL 2006 – REVISED APRIL 2013

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Control Inputs and Indicator Outputs

SERIAL DATA RATE SELECTOR

The Serial Data Rate Selector (RATE [1:0]) permits the user to fix the operating serial data rate. The pins have

internal pull-downs which maintain a logic-low input condition unless externally driven to a logic-high condition.

This input also serves to place the device in a test mode. The codes shown in Table 2 select the desired

operating serial data rate. The LMH0046 then enters either the Auto-Rate Detect mode or a single operating rate.

Selecting the 270 Mbps rate mode may also be used when reclocking DVB-ASI data. DVB-ASI data is MPEG2

coded data that is transmitted in 8B10B coding. The device will reclock this data without harmonic locking. Auto-

Rate Detect mode may be used for any supported data rate, including DVB-ASI.

Table 2. Data Rate Select Input Codes

Rate [1:0]

Data Rate

Comments

Code

or Mode

00

Auto-Rate Detect mode

143 Mbps rate operation supported only in ARD mode

01

270 Mbps

May be used to support DVB-ASI operation

10

1483/1485 Mbps

LOCK DETECT

The Lock Detect (LD) output, when high, indicates that data is being received and the PLL is locked. LD may be

connected to the MUTE input to mute the data and clock outputs when no data signal is being received. See

Table 3.

MUTE

The MUTE input, when low, mutes the serial data and clock outputs. It may be connected to Lock Detect or

externally driven to mute or un-mute the outputs. If MUTE is connected to LD, then the data and clock outputs

are muted when the PLL is not locked. This function overrides the Bypass function: see Table 3. MUTE has an

internal pull-up device to enable the output by default.

BYPASS/AUTO BYPASS

The Bypass/Auto Bypass input, when high, forces the device to output the data without reclocking it. When this

input is low, the device automatically bypasses the reclocking function when the device is in an unlocked

condition or the detected data rate is a rate which the device does not support. See Table 3. BYPASS/AUTO

BYPASS has an internal pull-down device.

Table 3. Control Functionality

LOCK DETECT

OUTPUT MUTE

BYPASS/AUTO BYPASS

DEVICE STATUS

0

1

0

PLL unlocked, reclocker bypassed

1

1

0

PLL locked to supported data rate, reclocker not bypassed

X

0

X

Outputs muted

0

LOCK DETECT

X

Outputs muted

1

LOCK DETECT

0

PLL locked to supported data rate, reclocker not bypassed

1

LOCK DETECT

1

PLL locked to supported data rate, reclocker bypassed

X

1

1

Outputs not muted, reclocker bypassed

SD/HD

The SD/HD output indicates whether the LMH0046 is processing SD or HD data rates. It may be used to control

another device such as the LMH0002 cable driver. When this output is high it indicates that the data rate is 270

Mbps (or 143 Mbps). When low, the indicated data rate is 1483 or 1485 Mbps. The SD/HD output is a registered

function and is only valid when the PLL is locked and the Lock Detect output is high. When the PLL is not locked

(the Lock Detect output is low), the SD/HD output defaults to HD (low). The SD/HD output is undefined for a

short time after lock detect assertion or de-assertion due to a data rate change on SDI. See Figure 6 for a timing

diagram showing the relationship between SDI, Lock Detect, and SD/HD.

10

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