Two bit parallel signal

kingneb

How do you concatinate four two bit values onto the end of one another? I have a signal coming from the PC's parallel port two bits at a time. I need to assemble those four two bit values as a byte.

Thank you

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Too many lies from the right, which is the wrong side of the tracks.

Post Edited (kingneb) : 11/2/2005 10:59:56 PM GMT

Jon Williams

Didn't we go through this already? And through a looonngg, drawn-out, often vague discussion?

--> http://forums.parallax.com/showthread.php?p=553414

You have two know when you have your two bits -- which means you actually need a third signal (latch, strobe, whatever you want to call it) unless you can guarantee that there will always be a bit change. In either case, grab the bits, shift them to their proper position, OR them with the final result.

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Jon Williams
Applications Engineer, Parallax

Post Edited (Jon Williams (Parallax)) : 11/2/2005 10:54:11 PM GMT

Bean

Which is it, first you say four two bit values, then you say two four bit values ???
Bean.

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kingneb

Sorry, I worded it in reverse. Its been a long day.

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Too many lies from the right, which is the wrong side of the tracks.

Post Edited (kingneb) : 11/2/2005 11:00:38 PM GMT

kingneb

What do we use as a bit shift operator?

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Too many lies from the right, which is the wrong side of the tracks.

Jon Williams

>> shifts right, << shifts left.

Both are in the help file -- please have a read (see Reference -> Operators)

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Jon Williams
Applications Engineer, Parallax

kingneb

x var byte
y var byte
result var byte

x = 3
y = 2

result = x >> y

would this assemble a nibble properly? I know this is not the full byte however I want to see If I have the right idea. I never had to use bitwise operations this etensively before.

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Too many lies from the right, which is the wrong side of the tracks.

Jon Williams

I suggest you fire up your compiler and run the program through Guenther's simulator (there's a button for it on the toolbar). Use RB or RC as your result variable so that you can see it in the output panel (make sure you make the select port bits outputs). Note that to do this you don't even need to have your SX connected. This will be a far more valuable experience for you.

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Jon Williams
Applications Engineer, Parallax

kingneb

This statement moves the two bit unit over to the highest position in the byte:

tris_b = 0
rb = 0
unit1 var byte
unit2 var byte

unit1 = 3
unit2 = 2

rb = unit2 << 6

This statement moves the two bit unit over to the second highest position:

tris_b = 0
rb = 0
unit1 var byte
unit2 var byte

unit1 = 3
unit2 = 2

rb = unit2 << 4

How do you move unit1 to the highest position and unit2 to the second highest position? The result should be 11100000.

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Too many lies from the right, which is the wrong side of the tracks.

Jon Williams

You're getting four groups of two bits, right? Well, then, you're going to have to do a multi-step process:

result = 0
result = result | (bitsIn1 << 6) <-- these are the highest bits
result = result | (bitsIn2 << 4)
result = result | (bitsIn3 << 2)
result = result | (bitsIn4) <-- these are the lowest bits

Please understand that this is pseudo-code to demonstrate the process; you'll have to clean it up to actually run it through the SX/B compiler.

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Jon Williams
Applications Engineer, Parallax

kingneb

No big deal

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Too many lies from the right, which is the wrong side of the tracks.