2 bytes to word array variable - fastest way

[MikeWinston]

Hello All,
I would like an "expert check" on this one....
I need to put 2 ADC bytes into a word variable thats part of an array.

This is what I have:
adcData var word[16]
adcData[index] = (ADRESH << 8) + ADRESL

Is there a better way (faster) ?

thanks,
Mike

P.S.
I am modernizing an old dehumidifier whose humidity sensor (tape strip) has
gone the way of the dodo. I figure get an electronic humidity sensor and I
would have another excuse for a PIC project.

[cncmachineguy]

Have you tested that? it seems like it will shift ADRESH 8 times, then assign it to the word. DOing it like that would be better I think like this:

adcdata[index] = ADRESH
adcdata[index] = adcdata[index]<<8
adcdata[index] = adcdata[index]+ADRESL

Not sure about that either.

I think you can do this:

adcdata.highbyte[index] = ADRESH
adcdata.lowbyte[index] = ADRESL

I am not certain on this, so my reply is as much a question as an answer. Hmmm, that sounds a little deep

OK, this I am certain about:

tempword var word
 
tempword.highbyte = ADRESH
tempword.lowbyte = ADRESL
adcdata[index] = tempword

[MikeWinston]

I have tested the code with VB.Net, and it works, but I haven't tested on the PIC yet.

I actually tried this code first but it did not compile:
adcData.highbyte[index] = ADRESH
adcData.lowbyte[index] = ADRESL
I guess you can't use the .lowbyte/.highbyte syntax on arrays.

Using the temp variable is probably the norm but I figure there might be some trick to doing
the same thing all nice and clean on one line.

[cncmachineguy]

In your VB test, Was ADRESH a byte or a word?

[MikeWinston]

Thanks Bert. I see what your getting at. ADRESH was a word.
I just tried ADRESH as a byte and had an overflow. oops, I missed that one.
I guess I'll use the temp variable way.

There is another way I used before:
adcData[index] = (ADRESH * 256) + ADRESL
But I would put money on this way is slower than the temp variable way.

[HenrikOlsson]

Hi,
Have you tried:

adcData.lowbyte[index] = ADRESL
adcData.lowbyte[index+1] = ADRESH

Take a look at Melanies writeup, specifically section 5, for further details.

/Henrik.

[scrwld]

hello, i use this and work:

read I,b1.HIGHBYTE ' read byte type var from EEprom
read I+1,b1.LOWBYTE 'read byte type var from EEprom
TEmpDs18(L) = B1 'word array

[MikeWinston]

Well it turns out the more intuitive way is also a little faster. That is if I
have done this correctly.

I used [view] [program memory] in MPLab and counted the number of
instructions between the start and end labels.

This code was 18 lines:

 
StartTest:
  adcData.lowbyte[Index] = ADRESL
  adcData.lowbyte[Index+1] = ADRESH
EndTest:

This code was 16 lines:

 
StartTest:
  tempWord.highbyte = ADRESH
  tempWord.lowbyte = ADRESL
  adcdata[index] = tempword
EndTest:

So as long as I can afford the extra word variable, I will be using the
temp variable way...... unless someone else reveals a clever trick.

thanks all for your replies,
Mike -

[mister_e]

If ADRESH & ADRESL are consecutive SFR... then you could use

    @ADRESULT = ADRESL
    ADRESULT VAR WORD EXT

    MyArray VAR WORD [8]

Start:
    MyArray[0] = ADRESULT

But I doubt ADRESL/ADRESH are consecutive in many PIC.

[MikeWinston]

mister_e,
Thats a good trick. One to remember. And it only produces 9 lines of
instruction. But your right, the PIC I'm using (16F684), ADRESH/L are not
next to each other.

Actually, ACCON0 is after ADRESH. That would give you an interesting result.

thanks,
Mike -