2

Application information

2.1

CEC line description

The CEC bus is described in the HDMI standards as the consumer electronics control. It provides control

functions between all the various audiovisual equipment chained in the user's environment.

The CEC block integrated in the HDMI2C1-6C1 implements a level shifter, shifting the cable CEC +3.3 V voltage

(VDD_CEC) down to the ASIC power supply voltage (VDD_IC) that can be as low as 1.8 V. The Figure 2 shows the

functional diagram of the integrated CEC block.

Figure 2. CEC link functional diagram

CEC_IC

VDD_CEC_IC

CEC

VDD_CEC

VDD_CEC_IC

VDD_CEC

CEC

driver

UVLO

Ctrl

circuit

Enable

HDMI

connector

decoupling

capacitance

In case of no activity on the bus, or if the CEC driver is off (VDD_CEC = 0), the output CEC pin is put in high-Z

mode (open circuit) protecting the circuitry and the application against hazardous backdrive.

The Figure 3 illustrates the normal operating mode of the CEC block when the IC from the source and when the

sink drives the communication.

Figure 3. CEC simplified

VDD_CEC_IC

CEC_IC

VDD_CEC

CEC

VTdown_CEC

VTup_CEC

VHYST_CEC

VDD_CEC_IC

CEC_IC

VDD_CEC

CEC

VIL_CEC_IC

VIH_CEC_IC

Block in high

impedance

Level shifting

Source IC drives

Sink drives through HDMI cable

Block in high

impedance

Block in high

impedance

Level shifting

Block in high

impedance

t

t

t

t

10%

90%

tFALL_CEC

tRISE_CEC

HDMI2C1-6C1

Application information

DS9943 - Rev 4

page 3/22