The TMDS442, 4-to-2 port DVI/HDMI switch, allows up to 4 digital video interface (DVI) or high-definition multimedia interface (HDMI) ports to be switched to two independent display blocks. The essential requirement of picture-in-picture display from two digital audiovisual sources is having two individual DVI or HDMI receivers in a digital display system. TMDS442 supports two DVI or HDMI receivers to enable multiple-source selection (picture-in-picture), as well as supports acting as a 4-input 1-output video switch.
Each input or output port contains one 5-V power indicator (5V_PWR), one hot plug detector (HPD), a pair of I2C interface signals (SCL/SDA), and four TMDS channels supporting data rates up to 2.25 Gbps. The 5-V power indicator and the hot plug detector are pulled down with internal resistors, forcing a low state on these pins until receiving a valid high signal. The I2C interface is constructed by an I2C repeater circuit to isolate the capacitance form both ends of the buses. TMDS receivers integrate 50- termination resistors pulled up to VCC, which eliminates the need for external terminations. An 8-dB input equalization cooperates to each TMDS receiver inputs to optimize system performance through 5-meter or longer DVI or HDMI compliant cables.
A precision resistor is connected externally from the VSADJ pin to ground, for setting the differential output voltage to be compliant with the TMDS standard for all TMDS driver outputs. The PRE pin controls the TMDS output to be operated under either a standard TMDS mode or an AC de-emphasis mode. When PRE = high, a 3-dB AC de-emphasis TMDS output swing is selected to pre-condition the output signals to overcome signal impairments that may exist between the output of the TMDS442 and the HDMI receiver placed at a remote location.
Each sink output port can be configured with the SA, SB, OE, I2CEN, and PRE pins. SA1, SB1, OE1, I2CEN1, and PRE1 regulate the behaviour of sink port 1; SA2, SB2, OE2, I2CEN2, and PRE2 regulate the behaviour of sink port 2. These control signals are hard-wire controlled by GPIO interface, or through a local I2C interface. When GE = low, the configurations are done through a local I2C interface, LC_SCL, LC_SDA, LC_A0, and LC_A1 pins, and the 5V_EN can be programmed through the local I2C interface. It is default high after device powered on. When GE = high, the configurations are done through GPIO pins regardless the value of the 5V_EN in the internal I2C registers.
The two bit source selector pins, SA and SB, determine the source transferred to the sink port. The internal multiplexer interconnects the TMDS channels and I2C interface from the selected source port to the sink port. The HPD output of the selected source port follows the status of the HPD_SINK. Since two of the source ports will always be unconnected to any output, the I2C interfaces of unselected ports are isolated and the HPD outputs of an unselected port are pulled low.
The TMDS outputs of each of the sink ports are enabled based on the OE signal and 5V_PWR signal (from the selected source port). When OE is low, for an output port, and the 5V_PWR signal from the selected source port is high, the TMDS output signals are enabled; otherwise they are disabled, and high impedance.
The I2C driver at sink side, SCL_SINK and SDA_SINK, are enabled by setting I2CEN high. When I2CEN is low, the I2C driver can not forward a low state to the I2C bus connected at the sink port. A hard wire output voltage select pin, OVS, allows adjustable output voltage level to SCL_SINK and SDA_SINK to optimise noise margins while interfacing to different HDMI receivers. The I2C driver of each source port, SCL and SDA, is controlled by its 5V_PWR signal. A valid 5-V signal appearing at the input of 5V_PWR enables the I2C driver of the source port.
The device is packaged in a 128-pin PowerPAD TQFP package and characterized for operation from 0°C to 70°C.
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