A DTV Supporting a Passive CEC Link

E-EDID Reading Configurations in Standby Mode

SINK

HPD1

SDA1

SCL1

A21/B11

A22/B12

A23/B13

A24/B14

HPD2

SDA2

SCL2

A21/B21

A22/B22

A23/B23

A24/B24

EQ

S1

S2

HPD_SINK

SDA_SINK

SCL_SINK

Y1/Z1

Y2/Z2

Y3/Z3

Y4/Z4

VSadj

VDD

(5V)

VCC

(3.3V)

GND

E-EDID

HDMI RX

DDC_SDA

DDC_SCL

Y1/Z1

Y2/Z2

Y3/Z3

Y4/Z4

5V

5V

47kW

47kW

mController

3.3V

4.7kW

4.7kW

CEC

CEC

4.02kW 10%

1kW

HPD

5V

SDA

SCL

CEC

CLK

D0

D1

D2

HPD

5V

SDA

SCL

CEC

CLK

D0

D1

D2

HPD

5V

SDA

SCL

CEC

CLK

D0

D1

D2

SOURCE 1

HPD

5V

SDA

SCL

CEC

CLK

D0

D1

D2

SOURCE 2

TMDS261

in different DTVs with different consumer electronic control (CEC) requirements. The CEC is an optional feature

of the HDMI interface for centralizing and simplifying user control instructions from multiple audio/video products

in an interconnected system, even when all the audio/video products are from different manufacturers. This

feature minimizes the number of remote controls in a system, as well as reducing the number of times buttons

must be pressed.

In Figure 34, the DTV does not have the capability of handling CEC signals, but allows CEC signals to pass over

the CEC bus. The source selection is done by the control command of the DTV. The user cannot force the

command from any audio/video product on the CEC bus. The selected source reads the E-EDID data after

receiving an asserted HPD signal. The microcontroller loads different CEC physical addresses while changing

the source by means of the S1 and S2 pins.

When the DTV system is in standby mode, the sources do not read the E-EDID memory because the 1-k

Ω

pulldown resistor keeping the HPD_SINK input at logic low forces all HPD pins to output logic-low to all sources.

The source does not read the E-EDID data with a low on HPD signal. However, if reading the E-EDID data in the

system standby mode is preferred, then TMDS261 can still support this need.

The recommended configuration sequences are:

1. Apply the same 3.3-V power to the VCC of TMDS261 and the TMDS line termination at the HDMI receiver

2. Because the TMDS261 has clock-detect circuitry and there is no valid input TMDS clock in the standby

mode, TMDS261 draws significanty less current.

3. Set S1 and S2 to select the source port which is allowed to read the E-EDID memory.

Note that if the source has a time-out limitation between the 5-V and the HPD signals, the foregoing configuration

is not applicable. Uses individual EEPROMs assigned for each input port, see Figure 35 through Figure 37. The

solution uses E-EDID data to be readable during system power-off or standby-mode operations.

Figure 34. Two-Port HDMI-Enabled DTV With TMDS261 – CEC Commands Passing Through

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