How recieve string into controller

 1.  	strcat(incom, bufIn);

>1. strcat(incom, bufIn);
>2. incom[i] = bufIn;
> i++;

How you declare "bufIn" ?

Function strcat need "pointer to char" (not a "char") as second parameter.
This must be NULL-terminated string with length less than unused area in "incom" !!!
So, your code probably have a bug or bug's.


I think this is not C251-specific question.



>Why I can't create any array of
>characters more than 20 symbols?

Why not ? No problem.

char       Buf[32]; // default memory space
// or
char idata Buf[64]; 
// or
char xdata Buf[1000]; 
// or
char edata Buf[32]; // C251-native addressing

Thank You for anser.
i thik i've understood my problem.
Thanks to all.

Sorry. I didn't found my mistake.
my code is:

bit Input = 0;
int i = 0;
unsigned char incom[18] = "";                  			
unsigned char bufIn[2] = "";
....
int PrntTo (unsigned char ch)
{
	TI = 0;
	SBUF = ch;
	while(!TI);
}

void port_io(void) interrupt 4 using 2 
{  
	 if (RI)
	{	
		bufIn[0] = SBUF;
		Input = 1;
	}
}
...
void main (void)  
{ 
...
	while(1)
	{	
		memset (incom, 0, 18);
		...
		while (Input)
		{
			PrntTo(bufIn[0]);
			RI = 0;
			Input = 0;

			strcat(incom, bufIn);
			i++;
			if(i == 17)
			{
				for(i = 0; i < 17; i++)
					PrntTo(incom[i]);
				i = 0;
			}
		}     
	}
...
}   

Your code includes several handling errors. I included my remarks in the code section.

bit Input = 0;
int i = 0;
/* initialized variables blow up the code size. Try to avoid them. */
unsigned char incom[18] = "";                  			
/* The buffer must have a size of 19 if you want to receive 18 characters. Since you handle the buffer as string, a trailing 0x00 is inserted. */
unsigned char bufIn[2] = "";
/* The second byte of bufIn is never set to 0x00. This must be done for the strcat()-function. */
....
int PrntTo (unsigned char ch)
{
	TI = 0;
	SBUF = ch;
	while(!TI);
/* TI generates in interrupt here. You must handle this IRQ somehow. */
}

void port_io(void) interrupt 4 using 2 
{  
	 if (RI)
	{	
		bufIn[0] = SBUF;
/* RI should be cleared immediately after reading SBUF. Otherwise you may lose a character. */
		Input = 1;
	}
/* Deal here to clear the TI-Interrupt-request. Easiest way: TI =0; */
}
...
void main (void)  
{ 
...
	while(1)
	{	
		memset (incom, 0, 18);
/* use sizeof instead of 18. This applies to all occurences of the buffer's size. */
		...
		while (Input)
		{
			PrntTo(bufIn[0]);
			RI = 0;
			Input = 0;
/* Setting this bit to 0 forces the controller to exit the while-Loop. Then the while(1)-loop is executed again, which clears your buffer again. All characters in the buffer are lost.... */
			strcat(incom, bufIn);
			i++;
			if(i == 17)
			{
				for(i = 0; i < 17; i++)
					PrntTo(incom[i]);
				i = 0;
			}
		}     
	}
...
}   

Your code not full...
I still don't understand it.
No hardware initialization sequence.
(serial port, interrupts, timers)

No sense to comment all of your code, just at first look:

- you must clear RI manually

 if (RI)
 {	
   RI = 0; // !!!

void port_io(void) interrupt 4 using 2 
{  
 if( TI ) {
     TI = 0;
    // etc
 }
 if (RI) {
     RI = 0;
    // etc
 }
}

 void port_io(void) interrupt 4 using 2 

>The buffer must have a size of 19 if
>you want to receive 18 characters

:)
This guy "want" to receive 17 (I think :)

  i++;
  if(i == 17)
  {
    for(i = 0; i < 17; i++)