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???
04/19/07 18:13
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 		 #137550 - Distortion
Responding to: ???'s previous message
The horizontal line scan rate varies, but is on the order of 30 KHz = 33us. With a 1K wide display, each pixel is about 33ns wide. So it does not take a lot of time variance to cause a multiple pixel wide distortion. Even a little 50/60 Hz noise on the master clock can be observed by eye.

That is why the video path is almost always done in logic, with the processor limited to updating memory.


List of 52 messages in thread
TopicAuthorDate
8051 to VGA            01/01/70 00:00      
   nope..... but i do know            01/01/70 00:00      
      Video            01/01/70 00:00      
         well, if throiughput is a problem            01/01/70 00:00      
         VGA vs. NTSC (OK, PAL)            01/01/70 00:00      
            especially on CRTs?            01/01/70 00:00      
               flicker            01/01/70 00:00      
                  Distortion            01/01/70 00:00      
                     until today...            01/01/70 00:00      
                        Logical Processors            01/01/70 00:00      
                           not likely ...            01/01/70 00:00      
                              sure, but what problem is that            01/01/70 00:00      
               It's the demand for precise timing            01/01/70 00:00      
                  Monochrome?            01/01/70 00:00      
                     He may be a bit misguided            01/01/70 00:00      
                  Ive used an spi interface            01/01/70 00:00      
                     This is the arbitary display overlay jobby            01/01/70 00:00      
      A NICE VIDEO GENERATING AND PROCESSING EXAMPLE!!            01/01/70 00:00      
         Is it VGA?            01/01/70 00:00      
   Video Buffer            01/01/70 00:00      
      and a "video DAC"            01/01/70 00:00      
         Well there are ways and ways ....            01/01/70 00:00      
            but VGA is twice as fast            01/01/70 00:00      
               VGA Pixel rate is faster but ...            01/01/70 00:00      
                  If the MCU can\'t do it all ...            01/01/70 00:00      
                     how about this one            01/01/70 00:00      
                        "stuffer"            01/01/70 00:00      
                           it'd better be a really cheap MCU            01/01/70 00:00      
                              why?            01/01/70 00:00      
                        the guy who pays for it would notice.            01/01/70 00:00      
                           why?            01/01/70 00:00      
                              The extra MCU contributes nothing. Why use it?            01/01/70 00:00      
                                 because            01/01/70 00:00      
                                    TEXT => Pixels = character generator            01/01/70 00:00      
                                       sure, but            01/01/70 00:00      
                                          True, but only sometimes ...            01/01/70 00:00      
                                             HUH?            01/01/70 00:00      
                                                so ... which MCU has those built in?            01/01/70 00:00      
                                                   those?            01/01/70 00:00      
                                                      Here's what "those" are ...            01/01/70 00:00      
                                                         options            01/01/70 00:00      
                                    working examples            01/01/70 00:00      
                     Nice to think folks remember Don's "cheap video"..            01/01/70 00:00      
                        What do you mean, Phillip?            01/01/70 00:00      
                           A notion not to radical or heretical ...            01/01/70 00:00      
                              I still think it's either/or and not both            01/01/70 00:00      
      Like the vhdl that you'll find            01/01/70 00:00      
         Here's an ARM7 Driving a VGA Display direct            01/01/70 00:00      
   75 Ohm?            01/01/70 00:00      
      75 Ohm it is...            01/01/70 00:00      
   dc motor            01/01/70 00:00      
      start a new thead - and be specific            01/01/70 00:00      

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