How does a monitor know to go to sleep?


Just an interesting question that I cannot find an answer too and it is bugging me.

When I put my computer to stand-by mode, my monitors automatically go into sleep mode and the green power lights go orange.

likewise when I set the power options in the control panel.

How does the monitor know that it needs to go to sleep. Example,

Do monitors have a processing chip or something to accept and react to commands.
Does the computer send a software command and the monitor receive it?
Does the video card cut the power output and the monitor knows this and reacts accordingly.

This is different that just pulling the video cable, as that causes a "check cable" on the monitor, as opposed to a "entering sleep mode" message.

I would love to get an answer as I haven't got any sleep for days trying to understand....... LOL


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SalvosgConnect With a Mentor Commented:
Here is some info on the 15 pin highdesnsity cables,

VGA=Video Graphics Adapter or Video Graphics Array.
VESA=Video Electronics Standards Association.
DDC=Display Data Channel.

Videotype: Analogue.

(At the videocard)
(At the monitor cable)

15 PIN HIGHDENSITY D-SUB FEMALE at the videocard.
15 PIN HIGHDENSITY D-SUB MALE at the monitor cable.

Pin Name Dir Description
1 RED Red Video (75 ohm, 0.7 V p-p)
2 GREEN Green Video (75 ohm, 0.7 V p-p)
3 BLUE Blue Video (75 ohm, 0.7 V p-p)
4 RES - Reserved
5 GND Ground
6 RGND Red Ground
7 GGND Green Ground
8 BGND Blue Ground
9 +5V +5 VDC
10 SGND Sync Ground
11 ID0 Monitor ID Bit 0 (optional)
12 SDA DDC Serial Data Line
13 HSYNC or CSYNC Horizontal Sync (or Composite Sync)
14 VSYNC Vertical Sync
15 SCL DDC Data Clock Line

Note: Direction is Computer relative Monitor.
Contributor: Joakim Ögren
Source: IEEE
Please send any comments to Joakim Ögren.
As far as I know it comes from the Operation System. It basically quits sending a signal to the monitors and they just go to sleep, same as if you had dual monitors and you had them both plugged in, but in the control panel you turned one of them off. It would be the same thing.
Plaintree_SystemsAuthor Commented:
Hi, Thanks for the answer,

my though would be this, if it came from the OS and just quit sending a signal, wouldn't the "check signal" error message show up as it does when you disconnect the cable and terminate the connection.

There must be something different that a complete signal termination?

No, because that is on a different line, your monitor cable has many pens, they all do various things as explained here . They don't come out and tell which one causes the monitory to say no monitor detected, but it looks like if the ground is not connected then it will cause the "check signal" that you are talking about.
Plaintree_SystemsAuthor Commented:
Thanks you sir, I am at rest with this issue. Appreciated
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