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Simple Casting

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beaker404

Joined: 24 Jul 2012
Posts: 163

Simple Casting

Posted: Mon Apr 29, 2019 4:01 pm

So simple I am embarrassed to ask.

Code:

pretrigger_value = 1234;
MSB = (int)(pretrigger_value>>8); // MSB
LSB = (int)pretrigger_value; // LSB

runs but does not give correct numbers. MSB = 4 and LSB -46 are what I get.

pretrigger_value is defined as INT16.

MSB and LSB are INT8.

What is the correct way to get the MSB and LSB from and INT16? and is there a more efficient way to do it than the >> operator?

CCS 5.064
Windows 10
running 18F87K22 at 60MHz

newguy

Joined: 24 Jun 2004
Posts: 1909


Posted: Mon Apr 29, 2019 4:03 pm

Look at make8()

PCM programmer

Joined: 06 Sep 2003
Posts: 21708

Re: Simple Casting

Posted: Mon Apr 29, 2019 4:37 pm

beaker404 wrote:

So simple I am embarrassed to ask.

Code:

pretrigger_value = 1234;
MSB = (int)(pretrigger_value>>8); // MSB
LSB = (int)pretrigger_value; // LSB

runs but does not give correct numbers. MSB = 4 and LSB -46 are what I get.

pretrigger_value is defined as INT16.

MSB and LSB are INT8.

It's all in your interpretation. You like to use signed decimal printouts,
but you're really dealing with the hexadecimal world. If you stay in hex,
most of your problems will go bye-bye.

1234 is 0x4D2 (using Windows 7 Prof. calculator in Programmer mode).

So 0x0D2 is the lsb. So select Hex and Byte (two different radio buttons
in Windows 7 calculator). Then type in D2. Then select Decimal and it now displays: -46
So -46 is correct.

beaker404

Joined: 24 Jul 2012
Posts: 163


Posted: Mon Apr 29, 2019 9:12 pm

Thanks, I knew I was just missing the obvious. I should not code during hay fever season.

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