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Propeller VGA — Parallax Forums

Propeller VGA

NewzedNewzed Posts: 2,503
edited 2006-08-06 23:27 in Propeller 1
Are the eight VGA LEDs found on the Propeller Demo board essential for proper operation of the VGA?

Thanks

Sid

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2006-08-06 23:00
    I don't think so. When Chip originally posted the VGA driver, there was no requirement and, from the way these simple D/A converters work, there is no need.
  • NewzedNewzed Posts: 2,503
    edited 2006-08-06 23:17
    Thanks, Mike.· I made a little adapter board so I could connect my VGA to my old Propeller board, which only had a TV output.· The little board is working greatand I now have a VGA.· It has an 8-pin male header and plugs right in to Pins 16-23.· Next thing is to·make a little adapter board so I can hook up my keyboard.· Had one before but it was just breadboarded and patched to the Propeller.· A little board that would plug into Pins 12 and 13 would be much neater.

    Incidentally, I was out of the 240 ohm resistors so I used 270 for the VGA - guess the resistor network is not too critical.

    Sid
  • Mike GreenMike Green Posts: 23,101
    edited 2006-08-06 23:27
    Yeah, the ratio of the resistors is more important than the absolute value. These are 4 level D/A converters with the ends of the resistor string either at 3.3V (3.3V output) or at 0V (0V output) or one end at 3.3V and the other at 0V with the resistor divider setting the midrange output voltage at either 1.1V or 2.2V depending on which bit is high and which is low (470 ohm is about twice the 240 ohm value for a 1/3 or 2/3 divider). On the sync pins, the resistors are just used for protection and any value from around 220 to 1000 ohms could work.
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