Questions/Basic/16F628A

I am building firmware for this pic to interface it with a Vector 2VXe compass module. The datasheet states the basic Datagram Structure to be

Sync Flag
0xAA
Frame Type
0xXX (example 0x01)
Terminator
0x00

If I am using pbp and the shiftin(out) commands, how exatcly do I format the data? Do I send the bit representation of the hex (example: 170 for 0xAA), or could I simply shiftin(out) a variable that contains a string like "0xAA"?

I have a rough draft that I threw up in a couple of days, and now I am going back to fix the areas that I needed more information on. Could I post my code? Its about 700 lines long.

One, more thing....How many bytes are in a word for this particular mcu. Since it's an 8bit mcu, its two bytes right?

tap tap tap... is this thing on? One more thing. Does anyone have any experience or code to share on how to convert a floating point number in basic? The output of the Vector compass is in IEEE 754 format, so I assume I have to convert this to a usable format in basic.

Quote:

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Originally Posted by BertMan

One, more thing....How many bytes are in a word for this particular mcu. Since it's an 8bit mcu, its two bytes right?

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Done some research on this and an 8 bit mcu means 8 bits to a word, which is the largest value the mcu can process. So, my next question is, how do I know when to set the variable to type word instead of byte when they both represent the same size - 8 bits?

Am I posting in the wrong forum? Are my questions too stupid to answer? Am I on the right site? Or perhaps my questions are beyond the scope of the members here? Maybe I just dont have enough patience to wait for a response? Do I need to stfu and rtfm? Maybe someone could enlighten me before I go crazy talking to myself :-)

I've never used it so I can say how it works but there is code on ME Lebs website for performing floating point. I stay away from FP just for headache sake.

And yes there are 2 bytes to a word.

Bit is a Bit
Byte is 8 Bits
Word if 2 Bytes or 16 Bits

Quote:

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Originally Posted by CocaColaKid

I've never used it so I can say how it works but there is code on ME Lebs website for performing floating point. I stay away from FP just for headache sake.

And yes there are 2 bytes to a word.

Bit is a Bit
Byte is 8 Bits
Word if 2 Bytes or 16 Bits

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Yep came across that code. I will be picking it apart this evening to see if it can help me. Unfortunately, I cant stay away from floating point because this is what the v2xe outputs.

Word is 2 bytes? I searched and read forever last night and the only definite conclusion I could reach was that it depends on the archietecture. Since my mcu is 8 bit, does this not mean 8 bit is the highest word the mcu can process?

Still working on it but here is what I got so far. I havent finished the menu system, nor have I figured a way to convert the floating point numbers coming from the V2Xe.

It might help to look at Melabs site .......

http://www.melabs.com/resources/fp.htm

Excellent! There is a subroutine to convert 32bit floats to a usuable ascii format. Hmm.. I dont think the 628 will hold all that code.

You could try using the 648, it has 4k.

I ended up using a math co-mcu to do the conversions. This little 8 pin device can convert strings, floats, and longs using the spi interface and only cost me $14. Here is the link: http://www.sparkfun.com/shop/index.php?shop=1&cat=79. Its the umFPU v2.0. I think the cost justified the headaches of using microcode's floating routines, and you can convert a string to float in about 3 lines of code, so I can still use the 628...YEAH!!! Attached is an alpha version of code that I am waiting to test as soon as the device gets here. You can see floating and long conversions in the routines: FloatToString, ConvertSInt32, and SetConfigMenu.

Conclusion to this thread: If you want an easy to use method for floating point conversion in the IEEE754 format, get a fp co-mcu.