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How to convert a char to an int ?

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John_Lintern

Joined: 30 Sep 2004
Posts: 14

How to convert a char to an int ?

Posted: Thu May 05, 2005 6:00 am

I am receiving ASCII characters from the RS232 receive port.

An interrupt occurs to store the received string.

However, to calculate the checksum I need the received ASCII characters to be converted to an int.

The two lines of code....

Code:

EvenChkSum=RxBuffer[r]^EvenChkSum;

and

Code:

OddChkSum=RxBuffer[r]^OddChkSum;

keep producing the value 0x00.

Presumably this is because the array RxBuffer[] is declared as a char.

So How can I convert the char to an int ?

My program so far looks like this.....

Code:

#include <16C74.h>
#device adc=8
#use delay(clock=20000000)
#fuses NOWDT,HS, PUT, NOPROTECT
#use rs232(baud=115200,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8, BRGH1OK)

#define Odd 0
#define Even 1

int i;
int Get_Version[16]={0x1E,0x00,0x0C,0xD1,0x00,0x07,0x00,0x01,0x00,0x03,0x00,0x01,0x60,0x00,0x72,0xD5};
int r=0;
char RxBuffer[56];
int OddChkSum=0;
int EvenChkSum=0;
int1 ChkSumByte=Even;

#int_RDA
RDA_isr()
{
RxBuffer[r++]=getchar();

if (ChkSumByte==Even)
{
   EvenChkSum=RxBuffer[r]^EvenChkSum;
   ChkSumByte=Odd;
}
else
{
   OddChkSum=RxBuffer[r]^OddChkSum;
   ChkSumByte=Even;
}
}

void main()
{

setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_psp(PSP_DISABLED);
setup_spi(FALSE);
setup_counters(RTCC_INTERNAL,RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
enable_interrupts(INT_RDA); // enable RS232 receive data interrupt
enable_interrupts(GLOBAL);    // enable all global interrupts

for (i=0;i<=56;i++)
{
   RxBuffer[i]=0;
}

// initialise phones UART by sending 0x55 (ASCII 'U') 128 times
for (i=0;i<128;i++)
{
   putc(0x55);
}
delay_ms(10);
for (i=0;i<=15;i++)
{
   putc(Get_Version[i]);
}

do
{
}
while(TRUE);

}

rwyoung

Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA

Posted: Thu May 05, 2005 7:23 am

Code:

EvenChkSum=RxBuffer[r]^EvenChkSum;

becomes

Code:

EvenChkSum=(int)RxBuffer[r]^EvenChkSum;

But in your case, "int" is still 8-bits, same as "char".

Look at the LST file created by your compiler and check for problems there. If necessary you can use an intermediate variable to hold the buffer value if the pointer dereferncing is causing a problem.

By the way, I don't see where you are preventing your index variable "r" from running past the end of your RxBuffer array. You should have some kind of limit test or use a power-of-2 length array and do some modulus arithmetic to get "r" to roll around.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

ckielstra

Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

Posted: Sun May 08, 2005 8:48 am

Code:

#int_RDA
RDA_isr()
{
RxBuffer[r++]=getchar();

if (ChkSumByte==Even)
{
EvenChkSum=RxBuffer[r]^EvenChkSum;
ChkSumByte=Odd;
}
else
{
OddChkSum=RxBuffer[r]^OddChkSum;
ChkSumByte=Even;
}
}

The 'r++' is causing your problems. A few lines later in the code your are refering to RxBuffer[r] which now points to an undefined value, by chance this was always zero in your tests.

Another bug:

Code:

for (i=0;i<=56;i++)
{
RxBuffer[i]=0;
}

You are clearing 57 bytes in a 56 byte RAM buffer...... Unpredicatble results will haunt you !

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