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Conversion of unsigned int to unsigned char

Waqas Ali Khan
Intellectual 570 points
Other Parts Discussed in Thread: CC430F5137, CC1101

Hello every one,

I am using cc430f5137, i am getting value from ADC12 which is unsigned int, now i want to transfer it through cc1101 module for which i need unsigned char value. In an ADC ISR i copied ADC12MEM2 value to num variable and then by using the memcpy command i want to convert it into char. when i try to look ch in Expression box it shows only "." can any one know how to convert it.

  • 0
    Guru 74080 points

    The "." looks like it is shown as ASCII. In the expressions box, right click on the variable -> Number format and select the desired format.
    But what do you want to have as value? Do you want chars? This would mean you will have to split your 12-bit value of the ADC12 into four seperate ASCII characters. 1012 would lead to '1' '0' '1' '2'. Or do you want to reduce the 12-bit value to an 8-bit one?

  • 0 in reply to Dennis Eichmann
    Intellectual 570 points
    Since unsigned int is of 16 bits and unsigned char is of 8 bits, so i want to see converted int value into character value i.e.
    if i an integer = 0xfedc
    then ch an char shows like ch[0] = 0xfe ch[1] = 0xdc
    i checked the number format and on by clicking the String option it only shows ")" and nothing else.
    What actually i want to say that i need 8 bits to transfer so for that i need to convert int into char, that's all.
  • 0 in reply to Waqas Ali Khan
    Guru 74080 points

    String format is ASCII - you want hex.

    Anyway - you want to split your 16 bits into two 8 bits - this is done by

    uint16_t adc_value = 1012; // In HEX: 0x03F4

uint8_t high_byte, low_byte;

high_byte = (adc_value >> 8);
low_byte  = adc_value;

  • 0 in reply to Dennis Eichmann
    Guru 58965 points
    May be the procedure itoa is needed.
  • 0 in reply to old_cow_yellow
    Guru 74080 points

    old_cow_yellow said:
    May be the procedure itoa is needed.

    I don't think so because

    Waqas Ali Khan said:
    if i an integer = 0xfedc
    then ch an char shows like ch[0] = 0xfe ch[1] = 0xdc

    looks like if he just want to split his 16 bits into two 8 bits.

  • 0 in reply to Dennis Eichmann
    Guru 23000 points

    An efficient way (no extra code needed) to Read/Write a Byte, From/To an Integer, is to use a 'union'.

    typedef struct HighLowByte {
	unsigned char	Low;
	unsigned char	High;
} HighLowByte;

typedef union UnsignedIntegerByte {
	unsigned int	Integer;
	HighLowByte		Byte;
	unsigned char	Array[2];
} UnsignedIntegerByte;

UnsignedIntegerByte	ADCvalue;
unsigned char	test;

int main(void) {
	WDTCTL = WDTPW + WDTHOLD; // hold WDT

	ADCvalue.Integer = 0x1234;
	test = ADCvalue.Byte.Low;
	test = ADCvalue.Array[0];	// same value as Low-byte
	test = ADCvalue.Byte.High;
	test = ADCvalue.Array[1];	// same value as High-byte

}

  • 0 in reply to Leo Bosch
    Guru 74080 points
    Interesting - never used it that way. Thanks for sharing!
  • 0 in reply to Dennis Eichmann
    Intellectual 570 points
    itoa is not found in stdlib.h file, can you please mention it in which header file it is found.
  • 0 in reply to Waqas Ali Khan
    Guru 12050 points

    If you don't need typedef (though typedef are great to make it a easy extern globaly)

    volatile union
{ unsigned int adcvalue;  
  struct{
    char low;
    char high;
  }adc_byte;
};

adcvalue = ADC12MEM;
UCB0TXBUF = adc_byte.high;
UCB0TXBUF = adc_byte.low;

    But if you like typedef place this in common.h

    typedef struct myintTag{
  char low;
  char high;
} myintstruct;

typedef union int_bytes { 
 unsigned int Integer;
 myintstruct Byte;  
}int_bytes;

extern int_bytes ADC12; // just one now, but this typedef can be reused over and over.

    and in main you can do this:

    #include 	"msp430.h"
#include 	"common.h"
int_bytes ADC12;

int main( void )
{...
  ADC12.Integer = ADC12MEM;
  UCB0TXBUF = ADC12.Byte.low;
  UCB0TXBUF = ADC12.Byte.high;

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