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DVI transferring VGA is wrong causes only one of the two monitors which are supported by the TC can display normally

Publication Date:  2012-11-20 Views:  40 Downloads:  0
Issue Description
There is a desktop cloud with the version of V100R002COOSPC200 in China Unicom, they use the TC with the version of EI945 to support the double-screen function, there is the DVI-I monitor outlet at the side of the TC, the DVI-I cable can support both the DVI and VGA outputs. Because there is only one kind monitor which has the VGA interface in the business hall, so they use a conversion adapter to transfer the DVI to VGA to connect the DVI output to the VGA monitor, then only one monitor which is connected with the VGA output can displayed normally, the one which is connected through the conversion adapter can’t display normally all the time.

Alarm Information
None
Handling Process
Validate the monitor connected with the TC in site.
1. Take a DVI input monitor and a VGA input monitor, connect the two monitors with the DVI-I connection cable, both the two monitors display normally. The connection cable sketch map is as followed:

2. Use the conversion adapter which transferring the DVI into VGA, connect to the VDI interface of the TC and the VGA monitor, it displays normally. The connection cable sketch map is as followed:

3. Use the DVI-I double-head cable bring by the TC’s own, the VGA interface connects to the VGA monitor, and the DVI interface connects to the conversion adapter as the 2nd step used, and then connects to the other VGA monitor. We find only one monitor which is connected with the VGA interface can display normally, and the one connected with the conversion adapter can’t display normally. The connection cable sketch map is as followed:

From the validation we can confirm that the conversion adapter can’t transfer the DVI signal into the VGA signal, the conversion adapter just abstracts the VGA simulation signal from the DVI-I interface and then output it to the monitor.
Solution:
The converter which transfers the DVI to VGA can actualize transferring the DVI digital signal into VGA simulation signal, it can used to connect the VGA monitor, and the converter is a active device, as the following picture displayed:

Root Cause
There are two group outputs signals contained in the interface of the EI945 TC’s VDI-I monitor: one group is the standard DVI digital output signal, it is used to connect with the standard VDI monitor; the other is the VGA simulation output signal, it is used to connect with the VGA monitor. Normally, we can use the standard DVI-I cable to connect the TC, the cable will divide into two kinds of interface, one end is the DVI interface, it can connect with the DVI monitor, the other end is the VGA interface, it can connect with the VGA monitor.
Because there are only the VGA monitors in site, we need to transfer the signal at the DVI interface into the VGA signal, so we use the conversion adapter to actualize it, and then connect it to the VGA monitor, the conversion adapter which transferring the DVI into VGA is as the following picture:

In fact, this type conversion adapter can only extract the VGA signal from the DVI-I, it can’t transfer the DVI digital signal in the DVI-I into the VGA simulation signal.
Suggestions
There are three types of monitor connection interface in the TC: DVI-I interface, VGA interface and DVI-D interface, we should understand the actual signal types outputted from these interfaces, and the necessary devices while transferring between them.

END