Whats the quickest way to set bits?

[bearpawz]

I am trying to create a bargraph display. It has 16 segments. My routine uses a calculation of an upper bound limit for what the display should be reading and a lower bound limit.

GraphDivider = (GraphMax - GraphMin)  / 16
GraphVal = (X / GraphDivider)

Everything to do with this graph is using word variables.

So lets say my graph top value is 100, and my graph lower value is 0, and X = 50:
(100 - 0) / 16 = 100 / 16 = 6.25
50 / 6.25 = 8

Thats exactly the result I expect to get. Now, to display the number 8 on the graph (having the first 8 LED's lit, the binary number I would have to send would be %0000000011111111

Is there a way to tell pic basic to set the first 8 bits on? Looking through the documentation I see I can set bit 8 with DCD=7 but that will leave all other bits at 0

[mackrackit]

How is the display connected to the MCU? How are you sending data to it.

[bearpawz]

Using an alegro A6276, so the pic shifts the data out. The displays thems selfs are working fine. I was just wondering if there was a quicker way to set all bits up to a certain bit number on with out having to use a look up table.

[Darrel Taylor]

<strike>GraphVal = $FFFF >> ((X * 16) / (GraphMax - GraphMin))</strike>

GraphVal = $FFFF >> (((X - GraphMin) * 16) / (GraphMax - GraphMin))
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[bearpawz]

DOH!

I knew there was something I wasnt thinking of...

The key was right shifting the $FFFF. If anyone else is following this, here is the final formula I came up with and it works perfectly.

GraphVal = $FFFF >> (16 - (X / ((GraphMax - GraphMin) / 16)))

This is for auto guages so the scale of the graph can swing. For instance, a fuel level gauge might read 0 to 16 galons, where a water temp guage might read 180° - 290°, so it was important to note that the bottom number might change as well as the top.

[Darrel Taylor]

And probably something I wasn't thinking of too.
That might go backwards, and need to be inverted.

GraphVal = $FFFF >> (16-(((X - GraphMin) * 16) / (GraphMax - GraphMin)))

I'll test it and see.

Doh, you beat me to it.
Oops again.

[bearpawz]

Uh Oh. Ok, it work flawlessly until you start working with a very tight scale. An example is the volt meter. It usually displays information from 8V to 18V with the guages I am replacing. Unfortunatly, based on the formula there ends up being too small of a number to even light one LED. (or at least its not lighting anything up). I passed in a value of 13 for my test data. This is a valid number between 8 and 18. However, when you start using the formula (the one I came up with) here is what happens:

GraphVal = (16 - (X / ((GraphMax - GraphMin) / 16)))

GraphVal = (16-(13/((18 - 8)/16)))

GraphVal = (16-(13/(10/16)))

GraphVal= (16-(13/.625)

GraphVal = 16-20

GraphVal = -4!


Sorry, Ive never been horribly great at actual math. Now what? lol.

[mackrackit]

You will not be getting a value volts at the ADC. You will have something between 0 and 255 or 0 and 1023. 8 or 10 bits.

So maybe we should start there.