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To reduce the transitions, it uses an advanced formula (algorithm) that converts 8 bit data into 10 bit data. Differential circuitry is then used to output complimentary signals. The results are… • Reduced Electromagnetic Interference (EMI). • Faster transfer rates with reduced errors. • Ability to use twisted pair wire vs. coax. A TMDS link consists of a TMDS Transmitter that encodes and sends a data stream to a TMDS Receiver, see Figure 10. Three sets of twisted pair wires carry the Red, Green and Blue data. An additional twisted pair carries the timing clock signal. Because the bandwidth over copper wire is limited to about 165 MHz, DVI can use up to two TMDS links, or 6 channels sharing the same clock. DVI with a dual-link TMDS has a bandwidth that is doubled. 1080i HDTV, with a pixel rate of 1920 X 1080 at 30Hz can be supported by a DVI interface operating in the single-link mode. 7 8 Display Data Channel (DDC) The VESA standard Display Data Channel, shown in Figure 10, is part of the DVI specification. It is an I2C bus used for data communications between the two devices. The data can include information specifying the type of display device connected and can also be used to support copy protection. Figure 10: Single-Link TMDS Extended Display Identification Data (EDID) EDID is the VESA standard protocol used over the DDC so the display device can communicate identification about itself to the host device. The data, stored in memory in the display device, can include its resolution, sync timing and refresh rates, etc. It is part of the plug and play package. Figure 11: HDCP 9 High-bandwidth Digital Content Protection (HDCP) HDCP is a system designed to protect the outputs of a DVI device from being copied. The protection can be applied in various ways. • Unrestricted copies • Limited number of copies • Limited use of copies • No copies Since this is a optional element of DVI, both the host device and the receiving device must be properly equipped to function and provide the protected link between them. There are three parts within the content protection scheme. • Authentication… The host and receiver exchange data to confirm the receiver is authorized to receive the protected data. • Encryption/Decryption… After the host has verified the receiver, "keys" are provided that will allow the receiver to decrypt the data sent. • Renewability… Each receiver is given both a secret code and a non-secret identification number. If the host determines the secret keys have been tampered with, the receiver is denied authentication. The authentication process occurs over the DDC I2C bus shown in Figure 11. After authentication, the encrypted video data is applied to the TMDS encoder. The encrypted data sent over the DVI interface is then immune to "eavesdropping." Only the authorized display device can reverse the encryption afterwards. Hot Plug Detect (HPD) Another part of the plug and play package is the VESA standard Hot Plug Detect. A dedicated pin on the DVI connector is used by the display to let the host know it is plugged in. When the host device detects a High condition greater than 2.4 VDC (typically 5.0 VDC), it will read the EDID and start operation. If the potential falls below 2.0 VDC the TMDS transmitter is stopped. Digital Monitor Power Management (DMPM) DMPM allows several different levels of power management by detecting the presence of EDID and/or TMDS activity. One pin on the DVI connector is provided so the host can supply a 5 V source. The display has the option to use this supply to keep the DDC capable while the monitor is off. DVI Connectors There two types of DVI receptacles shown in Figure 12, DVI-D and DVI-I. Pin assignments are detailed in Table 6. It should be noted, the additional pins, C1-C5, arranged in the + shape on the DVI-I receptacle, are provided for analog signals. No DVIA connector is shown because DVI-A is generally associated with adapting VGA connectors to DVI-I. Figure 12: DVI Receptacles PIN SIGNAL PIN SIGNAL 1 TMDS Data 216 Hot Plug Detect 2 TMDS Data 2+ 17 TMDS Data 03 TMDS 2&4 Shield 18 TMDS Data 0+ 4 TMDS Data 4- (NA) 19 TMDS 0&5 Shield 5 TMDS Data 4+ (NA) 20 TMDS Data 5- (NA) 6 DDC Clock 21 TMDS Data 5+ (NA) 7 DDC Data 22 TMDS Clock Shield 8 Analog Vertical Sync (NA) 23 TMDS Clock+ 9 TMDS Data 124 TMDS Clock10 TMDS Data 1+ C1 Analog Red (NA) 11 TMDS 1&3 Shield C2 Analog Green (NA) 12 TMDS Data 3- (NA) C3 Analog Blue (NA) 13 TMDS Data 3+ (NA) C4 Analog Horizontal Sync (NA) 14 +5.0 VDC C5 Analog Ground (NA) 15 Ground (NA) Not used by MonitorLink Table 6 MonitorLink DVI Connector Some manufacturers use DVI-I connectors for DVID only. This is the arrangement used by MonitorLink. This configuration will not support analog connections. Therefore, any attempt to interface analog signals, no matter what form of DVIA or DVI-I cables or adaptors used, will not be successful. Looking at the pin assignments in Table 6, it should become obvious, the DVI-I connector used by Monit...

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