CRT operation

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

How does a CRT monitor decide the number of pixels per scan-line?

I understand the CRT receives a h-sync and a v-sync signal (along with
other info). With this info, the monitor can decide *when* to start a
new horizontal scan-line, but I don't see how it decides how often to
sample the colour signal and display a pixel on that line.

TIA
WonderNuts

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

WonderNuts <nospam@nospam.zork> wrote:

>How does a CRT monitor decide the number of pixels per scan-line?
>
>I understand the CRT receives a h-sync and a v-sync signal (along with
>other info). With this info, the monitor can decide *when* to start a
>new horizontal scan-line, but I don't see how it decides how often to
>sample the colour signal and display a pixel on that line.

They don't sample, and there's no "decisions". They are analog
devices. When the RBG signal voltages rise and fall, the drive to the
corresponding scanning beam (which strikes the appropriately-colored
phosphor on the screen) rises and falls proportionally. It's as
simple as that.

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

> I understand the CRT receives a h-sync and a v-sync signal (along with
> other info). With this info, the monitor can decide *when* to start a
> new horizontal scan-line, but I don't see how it decides how often to
> sample the colour signal and display a pixel on that line.

They don't.. the video card who sends the signal makes these decisions, bits
in graphics card's memory are converted to different level voltage by
so-called Digital-to-Analog (DAC) converter, then all the monitor has to do
is to display different intensity red, green and blue from the analogic
input that comes from the DAC behind these copper wires that connect the
display to your computer's graphics card / chip / chipset / magic breadbox.

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

joe smith wrote:

>>I understand the CRT receives a h-sync and a v-sync signal (along with
>>other info). With this info, the monitor can decide *when* to start a
>>new horizontal scan-line, but I don't see how it decides how often to
>>sample the colour signal and display a pixel on that line.
>
>
> They don't.. the video card who sends the signal makes these decisions, bits
> in graphics card's memory are converted to different level voltage by
> so-called Digital-to-Analog (DAC) converter, then all the monitor has to do
> is to display different intensity red, green and blue from the analogic
> input that comes from the DAC behind these copper wires that connect the
> display to your computer's graphics card / chip / chipset / magic breadbox.

That makes sense.

Thankyou to all who replied.