OSD using LM1881

[delene]

I am using the LM1881 to design a video overlay unit.

I am having a problem in that you have to continually send out the characters that need to appear on the screen.
I can get them to display, but the spacing between the characters is too great. I also need to display more than one line of text.

Does anyone have some sample text...

Many thanks
Delene

[Ian McCrum]

Hi, you may be in an area were machine code is necessary to ensure the timing is correct. I have built a couple of designs using PICDREAM, this is a text generator that displays a mono colour bar, and some scrolling text. - google for PICDREAM and you'll see it is done entirely in machine code - and must be instruction perfect. It generates all video signals, one 16F84, 5 resistors and a capacitor - a clever design!

on the other hand a 40MHz PIC might do it in C ....

To add text to an existing video image you may need to use a phase locked loop and sync the PIC clock to a multiple of the line frequency - this has been done before but I forget the url.

The common solution is to use a special OSD chip that is hard to get...

good luck
Ian
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Ian McCrum, email address held at
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