HDMI interface circuit device

Abstract

The utility model relates to an HDMI (High-Definition Multimedia Interface) circuit device, which serves HDMI information source end equipment and can provide virtual HDMI display configuration information for an HDMI information source circuit when an HDMI standard connector is not externally connected with an HDMI display. When the HDMI standard connector is externally connected with a real HDMI display, the HDMI information source circuit can still normally read the configuration information of the real HDMI display. No matter whether a real HDMI display is externally connected or not, the HDMI signal source circuit always considers to be connected with one HDMI display and automatically switches between the virtual HDMI display and the real HDMI display.

Description

Technical Field

[0001] The invention belongs to a HDMI interface circuit device, and in particular relates to an HDMI interface circuit device which automatically provides virtual display configuration information. Background Art

[0002] In the display field, HDMI has been widely used. HDMI has five pin types: A, B, C, D, and E. Currently, Type A is the most common in the market. Its signal definition is as follows:

[0003]

[0004] like Figure 1 As shown,

[0005] 1) PIN1-PIN 9 are the pins actually used for TMDS data transmission, divided into 3 groups: 0, 1, and 2.

[0006] 2) PIN 10-PIN 12 is the TMDS clock signal. If the current Video Timing is 480p@60Hz (Htotal: 800, Vtotal: 525), then TMDS clock = 800x525x60 = 25.2MHz. TMDS clock is like a packing of pixels. One clock transmits the R, G, B (8-bit) signal of one pixel in three channels.

[0007] 3) PIN 13 is CEC (consumer electronic control), which is similar to an extended HDMI function, allowing manufacturers to customize HDMI messages. (For example, if you have a DVD and a TV connected with an HDMI cable, if you can control the DVD with the TV's remote control and the DVD performs a certain function, then the command signal of the function is transmitted through the CEC pin between the TV and the DVD).

[0008] 4) PIN 14 is a reserved pin and is not used (or an extra pin can be provided for CEC).

[0009] 5) PIN 15-PIN 16 is I2C pin, used for DDC (Display Data Channel, mainly used for EDID and HDCP transmission) transmission. In the HDMI process, DDC communication is almost the first thing to do (with Hot plug before), because the master and slave devices of HDMI need to obtain the EDID of their counterparts through DDC, so as to obtain various information.

[0010] 6) PIN 17 is the ground pin.

[0011] 7) PIN 18 is the 5V pin.

[0012] 8) PIN 19 is the Hot plug (HPD) pin (used to monitor whether the HDMI device exists. If it exists (Hot plug is high), then the EDID can be read through DDC). HDMI stipulates that when the HDMI 5V is powered off, the HDMISource can read the EDID of the HDMI Sink, which means that the Hot plug needs to be High. Sometimes multiple HDMI channels are switched. After switching, the HDMI channel should be initialized first, that is, the Hot plug is pulled low first to notify the HDMI source that the EDID used before has changed and needs to be re-read. Then the HDMI source will read the new EDID when the Hot plug is pulled high, but the pulling process takes at least 100ms, otherwise the HDMI source may not read the new EDID.

[0013] It is common practice that each HDMI display device will have an EEPROM chip as EDID ROM to save this data. When the HDMI cable is hot-plugged, external HDMI source devices such as DVD players will read EDID data through the HDMI DDC channel. EDID mainly defines the image resolution, audio format, audio channel, and 3D supported by the display device. Its purpose is to tell the HDMI source device the features I support and let the HDMI source device output a timing I support. The HDMI specification stipulates that the first 128Byte of EDID must be a data structure that complies with EDID1.3, and the second 128Byte must be a CEAEDID timing extension data structure that complies with EIA / CEA-861B. The E-EDID data structure defined by CEA-861-D is supported in HDMIIP. DCC complies with the I2C protocol. EDID is stored in a ROM chip. The HDMI protocol stipulates that the I2C address of the ROM must be OxAO.

[0014] HDMI interface is also gradually being used in embedded devices. Some embedded devices, such as mobile robots, are generally only connected to an external HDMI display (HDMI Sink) during the debugging stage. It is not convenient to carry an HDMI display during actual operation. Instead, a remote desktop connection is made through a network, such as VNC Viewer, Remote DisplayProtocal, Sunflower remote control software and other software. Some remote desktop software requires the display of the embedded device to be in working state, so some people install a virtual HDMI display with only EDID ROM outside the HDMI connector, such as Figure 2 As shown, this virtual HDMI display pulls up the HDMI Hot plug (marked as HDMI_HPD) pin, and at the same time, the DDC signal composed of HDMI_SCL and HDMI_SDA is connected to the I2C interface of the HDMI source device. The I2C bus address of the EDID ROM is OXAO, and the TMDS data and clock signals are not connected. In this way, the software of the HDMI source device determines that there is an HDMI display connected to the HDMI connector, and the entire software system continues to work as if there is an HDMI display, which can meet the requirements of some remote desktop connection software.

[0015] The present invention further provides an HDMI interface circuit device. Regardless of whether a real HDMI display is connected to the outside, the HDMI signal source circuit always considers that an HDMI display is connected, and automatically switches between the virtual HDMI display and the real HDMI display. Summary of the invention

[0016] In view of the room for improvement in the prior art, the present invention provides an HDMI interface circuit device.

[0017] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0018] An HDMI interface circuit device comprises an HDMI standard connector, an EEPROM memory unit, a monostable circuit unit and an HDMI signal source unit.

[0019] The HDMI Hot plug signal is used as an address signal of the EEPROM memory. When the HDMI standard connector is not connected to an external HDMI display, the address of the EEPROM memory is equal to the HDMI DDC interface access address OxAO; when the HDMI standard connector is connected to an external HDMI display, the address of the EEPROM memory is not equal to the HDMI DDC interface access address OxAO.

[0020] The I2C bus of the DDC interface of the HDMI source unit is connected to the EEPROM memory unit and the HDMI standard connector at the same time.

[0021] The monostable circuit generates a monostable high-level signal with a low pulse in the process that the input Hot plug signal of the HDMI standard connection changes from low to high. The monostable high-level signal output by the monostable circuit is used as the input signal of the HDMI source unit, and is used to determine whether an external HDMI display is connected, and whether the HDMI DDC interface needs to re-read the display EDID information.

[0022] Regardless of whether there is a real HDMI display connected externally, the HDMI source circuit always assumes that it is connected to an HDMI display and automatically switches between the virtual HDMI display and the real HDMI display. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the signal connection diagram of HDMI source device (source) and display device (sink);

[0024] Figure 2 Provide a block diagram for an existing external virtual HDMI display;

[0025] Figure 3 It is a block diagram of the HDMI interface circuit of the present invention;

[0026] Figure 4 This is a signal circuit diagram of the HDMI connector of the present invention;

[0027] Figure 5 It is the EEPROM circuit diagram of the present invention;

[0028] Figure 6 It is a monostable circuit diagram of the present invention; DETAILED DESCRIPTION

[0029] An HDMI interface circuit is characterized by: an HDMI standard connector, an EEPROM memory unit, a monostable circuit unit, and an HDMI signal source unit.

[0030] like Figure 3 Most of the signals of the HDMI Type A standard connector are directly sent to the CPU, and some signals are connected to the additional EEPROM and monostable circuit to implement the technical solution of the present invention. Figure 4 This is the HDMI connector signal circuit diagram of the present invention, which has no difference with the HDMI Type A standard connector signal definition.

[0031] like Figure 3 and Figure 5 As shown, the HPD signal of HDMI is used as an address signal of the EEPROM memory. When the HDMI standard connector is not connected to an external HDMI display, the address of the EEPROM memory is equal to the HDMI DDC interface access address OxAO. This interface circuit can provide a display configuration information to the HDMI source circuit, so that the HDMI source circuit can work in the manner of having an external HDMI display.

[0032] When an external HDMI display is connected to the HDMI standard connector, the address of the EEPROM memory is not equal to the HDMI DDC interface access address OxAO. Therefore, the addresses are different, and the EEPROM on this interface circuit will not respond to the I2C read and write access of the HDMI source circuit. When an external HDMI display is connected to the HDMI standard connector, the HDMI source circuit can still read the display configuration information of the external HDMI display normally.

[0033] like Figure 5 , the schematic diagram of the EEPROM circuit unit can be understood by general electronic engineers and no further description is needed.

[0034] A monostable circuit is a basic pulse unit circuit with two working states: steady state and transient state. When there is no external signal trigger, the circuit is in steady state. When triggered by an external signal, the circuit flips from steady state to transient state, and after a period of time, the circuit automatically returns to steady state. The length of the transient time depends on the parameters of the circuit itself, and has nothing to do with the length of the trigger signal action time.

[0035] like Figure 3 The present invention requires a signal HPD_CPU which is a high level in a steady state to be given to the CPU, indicating that a real HMDI display or a virtual HDMI display is always in place. When an external real HDMI display is inserted, the HDMI_HPD signal input on the HDMI connector changes from a low level to a high level. This high-triggered monostable circuit generates a low pulse with a width of not less than 100ms during the process of the HDMI_HPD signal changing from low to high. The CPU, as an HDMI source circuit, will read the external HDMI configuration information EDID again through I2C after this signal changes from low to high.

[0036] About the realization of monostable circuit. Commonly used monostable trigger chips are: 74Is121, 74Is122, 74Is123, CD4098, CD4528, CD4047. These special circuits are easy to use. Electronic engineers can refer to the corresponding device data to complete. In addition, comparators and logic circuits can also be used to realize it. The present invention provides an embodiment of the realization of a 555 timer chip, such as Figure 6 As shown, in steady state, HPD_CPU is high level, indicating that there is a real HMDI display or a virtual HDMI display in place. When an external real HDMI display is inserted, the HDMI_HPD signal input on the HDMI connector changes from low level to high level, and HPD_CPU outputs a low pulse, and then returns to high level. The width of the low pulse is determined by the size of R53 and C116. By adjusting the size of these two devices, a width greater than 200ms can be achieved, meeting the HDMI requirement of at least 100ms.

[0037] The function of the 555 timer is mainly determined by two comparators. The output voltage of the two comparators controls the state of the RS trigger and the discharge tube. When a voltage is added between the power supply and the ground, when pin 5 is left floating, the voltage at the non-inverting input of the voltage comparator C1 is 2VCC / 3, and the voltage at the inverting input of C2 is VCC / 3. If the voltage at the trigger input TR is less than VCC / 3, the output of comparator C2 is 0, which can set the RS trigger to 1, making the output OUT = 1. If the voltage at the threshold input TH is greater than 2VCC / 3, and the voltage at the TR terminal is greater than VCC / 3, the output of C1 is 0, and the output of C2 is 1, which can set the RS trigger to 0, making the output low.

[0038] Figure 6 The functions of each pin of the 555 timer chip are as follows:

[0039] Pin 1: negative terminal of external power supply VSS or ground, usually grounded.

[0040] Pin 2: Low trigger terminal TR.

[0041] Pin 3: Output terminal Vo

[0042] Pin 4: It is the direct reset terminal. When this terminal is connected to a low level, the time base circuit does not work. At this time, no matter what level TR and TH are at, the output of the time base circuit is "0". This terminal should be connected to a high level when not in use.

[0043] Pin 5: VC is the control voltage terminal. If this terminal is connected to an external voltage, the reference voltage of the two internal comparators can be changed. When this terminal is not used, a 0.01μF capacitor should be connected to ground in series to prevent interference.

[0044] Pin 6: High trigger terminal TH.

[0045] Pin 7: Discharge terminal D. This terminal is connected to the collector of the discharge tube T and is used to discharge the capacitor when the timer is used.

[0046] Pin 8: External power supply VCC. The VCC range of bipolar timing circuit is 4.5~16V, and the VCC range of CMOS timing circuit is 3~18V. Generally, 5V is used.

[0047] The above is a detailed description of an embodiment of the utility model, but the content is only a preferred embodiment of the utility model and cannot be considered to limit the scope of implementation of the utility model. All equivalent changes and improvements made within the scope of application of the utility model should still fall within the scope of the patent coverage of the utility model.

Claims

1. An HDMI interface circuit device, Its characteristics are: The interface circuit device includes an HDMI standard connector, an EEPROM memory unit, a monostable circuit unit, and an HDMI source unit. The HDMI Hot plug signal is used as an address signal of the EEPROM memory. When the HDMI standard connector is not connected to an external HDMI display, the address of the EEPROM memory is equal to the HDMI DDC interface access address 0xA0. When the HDMI standard connector is connected to an external HDMI display, the address of the EEPROM memory is not equal to the HDMI DDC interface access address 0xA0. The I2C bus of the DDC interface of the HDMI source unit simultaneously connects the EEPROM memory unit and the HDMI standard connector.

2. The HDMI interface circuit device according to claim 1, Its characteristics are: The interface circuit device includes a monostable circuit, which generates a monostable high-level signal with a low pulse when the input Hot pIug signal of the HDMI standard connection changes from low to high. The monostable high-level signal serves as the input signal of the HDMI source unit.

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