In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Mayfield wrote:

I once built a Full Field Color-Bar Generator using a Pic with its Clock running with a standard 3.579545 MHz Color Crystal.
The same crystal signal was passed through an Op-Amp that drove a home made delay line with 6 adjustable taps. Each tap fed another Op-Amp that that I could control from the PIC to Pass the 3.58 Color signal for that particular color. 

Only One 'Color Bar' Amp was on at any one time. 

The output DC level of the Op-Amps was also adjustable, just how I'm not remembering, this was many moons ago. I think I chose using Op-Amps over Analog Switches for this reason.

Finally the Color information was added to the PIC Video generated stuff. 

 

Clear as Mud.

 

In other words for example, when generating the Red Color Bar the Red Op-Amp would be turned on and the total delay from the Crystal through the delay line and Op-Amps was such to produce the Red Signal. I should note, there was an additional Op-Amp used for the Burst Reference.

Sounds complicated but turned out fairly simple overall and adjusting the various delays to within 2 degrees was quick and easy using a Vectorscope.

The Delay Line resembled one of those straight adjustable Power Resistors, except with very fine wire. 

 

Using the same crystal for the PIC Clock and color signal greatly simplified the timing in the PIC Coding.

If I remember, the Burst was the most critical, I think I used 8 cycles, which is the lower limit.

 

I did use interlacing, I find that most video devices are very tolerant but some are not.

I can't remember that the code was all that more complicated for interlacing.

I do remember that the code was heavy with 'straight-line' coding (not a lot of subroutine calling), most calls were to delay routines and padded with nop's.

 

Tom M.

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=99302#m127256

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2006 (http://www.dotNetBB.com)