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ADV3002

Rev. 0 | Page 16 of 28

LOSS OF SIGNAL DETECT

The TMDS clock line of each HDMI input has a loss of signal (LOS)

monitor attached to it. The purpose of the LOS monitor is to

determine if there is activity in the HDMI link. A simplified

circuit diagram of the LOS detector is shown in Figure 27. The

LOS monitors are disabled by default. The LOS monitors can be

enabled by programming the LOS_EN bit of the LOS detect control

read in the LOS detect status register. A logic high LOS_STATUS

bit of a given HDMI input indicates an inactive input; a logic low

LOS_STATUS bit indicates an active input. Three conditions need

to be fulfilled for an HDMI input to be considered active:

•

The TMDS input termination resistors must be enabled. By

default, the ADV3002 TMDS input termination resistors are

enabled only on the selected input.

•

The TMDS clock frequency exceeds the frequency cutoff

(LOS_FC). Refer to Table 1 for the value of the LOS fre-

quency cutoff.

•

TMDS clock differential amplitude exceeds the LOS threshold

set in the LOS detect control register. Refer to Table 1 for the

value of the LOS amplitude threshold.

FREQUENCY

DETECTOR

FREQUENCY

DETECTOR

TMDS CLOCK

INPUT[x]

LOS_FC

LOS_THR

LOS_STATUS[3:0]

Figure 27. Loss of Signal Detect Simplified Circuit Diagram

LOS Autosquelch

The LOS detect circuit can be used to automatically disable the

TMDS signal path. Setting the LOS_RX_EN bit in the LOS

control register causes the selected TMDS input to be disabled

when an LOS event occurs on that input. In this case, the TMDS

signal path is enabled when the active signal conditions listed

previously are met.

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