Separate an 'int' into 2 'char's in C18?

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craigwllee

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c18 byte char int bit

Hi all, I'm working on a project that use Microchip PIC18 series. The only compiler I have is the C18 provided freely from microchip
Anyway it is a simple question. I have an unsigned int that I wish to break it into 2 char that I could send through UART using the putcUSART function. I'm thinking of using the union struct or something, but I can't find references online.
Anyone knows how to do it? Thanks
 

int char mcc18

Can you not use something like the following?

Code: 
	int	int_var;
	unsigned char high_char, low_char;
...
	high_char = int_var >> 8;
	low_char = int_var & 0xFF;

Added after 11 minutes:

Or a bit better method for getting the high byte:



Code: 
	int	int_var;
	unsigned char high_char, low_char;
...
	high_char = int_var / 256u;
	low_char = int_var & 0xFF;
Cheers,
 

    C

    craigwllee

    Points: 2
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c18 int

Code: 
typedef union combo {
	int Int;	   
	char Char[2];	   
} Tcombo;

Tcombo x;

x.Int = 0x1234;

x.Char[0] == 0x12; // NOTE! Only if the compiler uses big endian -
x.Char[1] == 0x34; // otherwise it is the other way around.
 

    C

    craigwllee

    Points: 2
    Helpful Answer Positive Rating
microchip c unsigned char int

The Tcombo thing is exactly what I want, I'm thinking the union method is more efficient than taking division and mod? (not sure)
Thank you both for the help =)
 

c18 high byte

Yes, the union method is much more efficient as it only involves moves -
no calculations or loops are necessary.

I've checked the C18 compiler now and it uses litlle endian so the resulting
high byte will be in Char[1]. Like this:

Code: 
x.Char[1] == 0x12; // High byte
x.Char[0] == 0x34; // Low byte

See section 2.2 in the manual: https://ww1.microchip.com/downloads/en/DeviceDoc/C18_User_Guide_51288j.pdf

/Ram
 

c18 char

craigwllee said:
The Tcombo thing is exactly what I want, I'm thinking the union method is more efficient than taking division and mod? (not sure)
Thank you both for the help =)
Click to expand...
Have a look at this thread to see you question answered:
**broken link removed**

C18 would not actually do the division or shifting. Why don't you try compiling those code snippets to see what is actually done? I do know about the union method, but I prefer the other two methods.

Cheers,
 

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