[rescue] VGA Scan Conversion

J. Alexander Jacocks jjacocks at mac.com
Thu Aug 18 15:29:45 CDT 2011

On Thu, Aug 18, 2011 at 4:17 PM, J. Alexander Jacocks <jjacocks at mac.com>
> On Thu, Aug 18, 2011 at 4:11 PM, Nate Raymond <nraymond at gmail.com> wrote:
>> On Thu, Aug 18, 2011 at 4:04 PM, J. Alexander Jacocks
<jjacocks at mac.com>wrote:
>>> I have a Dell 2001fp, which, though an otherwise excellent LCD (IPS
>>> panel, lots of inputs, etc.), claims to be multisync, but is not.  The
>>> specs are:
>>> Horizontal scan range   31 kHz to 80 kHz (automatic)
>>> Vertical scan range     56 Hz to 76 Hz, exception 1600 x 1200 at 60 Hz
>>> (from http://support.dell.com/support/edocs/monitors/2001fp/EN/specs.htm)
>>> But, I have found that it will not do 640x480 at 66 or 640x480 at 75, which
>>> are within it's supposed range.  I've found the same on several other
>>> LCDs that I own.
>> Are you sure it's not because the Dell 2001fp lacks sync on green?  Early
>> macs didn't have composite sync, they did sync on green, and some monitors
>> (like that NEC mentioned and quite often ViewSonic) support both composite
>> sync and sync on green, while Dell monitors don't support sync on green
>> (that I know of).
> Nate,
> No, the Dell LCDs that I have (2001fp, 2405fpw) both support SoG, as
> demonstrated by connecting them to my DEC 3000/400 AXP, which requires
> it.

At the risk of replying to myself, I found the following, linked from
the (hardly encyclopedic) Wikipedia entry, on "Multysync Monitor":

"If the video signal supplied to such a monitor is within the range of
it's deflection circuits, the image will be displayed; otherwise, the
image may be either not synchronized, or completely blanked. It is
also possible to harm some monitors of this type by applying a video
signal outside it's ranges, if protective measures were not put into
place by the design. Thus, such a monitor will usually operate at the
most common video modes, but may not operate at less common modes.
This type of monitor may be referred to as a 'banded' design. A
continuous frequency design should operate at any frequency within the
specified range."


That gives me a better term to use...what I'm now saying is that I
have not found an LCD monitor that is truly multisynchronous.  All the
monitors that I have tested are "banded", as discussed, above.

- Alex

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