CM2030

Rev. 5 | Page 6 of 17 | www.onsemi.com

When I

seen by the ASIC on DDC_XX_IN is equal to or lower than DDC_XX_OUT.

Multiport DDC Multiplexing

By switching LV_SUPPLY, the DDC/HPD blocks can be independently disabled by engaging their inherent

“backdrive” protection. This allows N:1 multiplexing of the low-speed HDMI signals without any additional FET

switches.

Consumer Electronics Control (CEC)

The Consumer Electronics Control (CEC) line is a high level command and control protocol, based on a single

wire multidrop open drain communication bus running at approximately 1kHz (See Figure 3). While the HDMI

link provides only a single point-to-point connection, up to ten (10) CEC devices may reside on the bus, and

they may be daisy chained out through other physical connectors including other HDMI ports or other dedicated

CEC links. The high level protocol of CEC can be implemented in a simple microcontroller or other interface with

any I/OD (input/open-drain) GPIO.

Figure 3. Typical µC I/OD Driver

To limit possible EMI and ringing in this potentially complex connection topology, the rise- and fall-time of this

line are limited by the specification. However, meeting the slew-rate limiting requirements with additional

discrete circuitry in this bi-directional block is not trivial without an additional RX/TX control line to limit the output

slew-rate without affecting the input sensing (See Figure 4).

Figure 4. Three-Pin External Buffer Control

Simple CMOS buffers cannot be used in this application since the load can vary so much (total pullup of 27kΩ to

less than 2kΩ, and up to 7.3nF total capacitance.) The CM2030 targets an output drive slew-rate of less than

100mV/ms regardless of static load for the CEC line. Additionally, the same internal circuitry will perform active

termination, thus reducing ringing and overshoot in entertainment systems connected to legacy or poorly

designed CEC nodes.

RX

TX

I/OD

GPIO

CEC

RX

TX

TX_EN

CEC

Slew Rate

Limited

3-State Buffer

X