Hi,
I am stuck up a peculiar problem while using 8051 external RAM.
I am declaring a variable: unsigned int xdata x _at_ 0xA004;
then I equate: x=6;
and i display this value on the hyperterminal (RS232) window using the function:
serial_num(x+0x30);
every thing goes fine and the value 6 is diaplayed on the hyper terminal window.
PROBLEM:
when i equate the value x to another variable *p and try to display the value *p i am unable to get the value on the hyper terminal window.
unsigned int xdata *p _at_ 0xA008;
x=6; p=&x; serial_num(*p+0x30);
when I try to display this on the hyper terminal (RS232) window I get garbage values displayed on the screen.
Here is the code that was developed.
#pragma LARGE #include<reg52.h> #include<string.h> #include<absacc.h> #include<intrins.h> #include<ctype.h>
sbit RXD_pin=P3^0; sbit TXD_pin=P3^1; sbit INT0_pin=P3^2; sbit INT1_pin=P3^3; sbit WRITE_pin=P3^6; sbit READ_pin=P3^7;
unsigned int xdata read_byte _at_ 0xA001, write_byte _at_ 0xA003; unsigned int xdata count _at_ 0xA005, *p _at_ 0xA007 , x _at_ 0xA009; unsigned int idata i; unsigned char xdata CS5_enable _at_ 0XA000; //CS5_enable is the variable declared to chip select the external RAM. Static RAM used is HY6264. 8K RAM unsigned char xdata CS2_enable _at_ 0x4000;
void read_ram(void); void write_ram(void); void serial_init(void); void serial_num(unsigned char); void delay(void);
void main(void) { serial_init(); while(1) { write_ram(); x=6; p=&x; write_ram(); write_byte=*p;//write value to external ram location read_ram(); read_byte=write_byte;//read value from external ram location serial_num(read_byte+0x30); //display on hyper terminal window screen } }
void read_ram(void) { CS5_enable=1; WRITE_pin=1; READ_pin=1; }
void write_ram(void) { CS5_enable=0; WRITE_pin=0; }
void serial_num(unsigned char s) { SBUF=s; while(TI==0); TI=0; }
void serial_init(void) { TMOD=0x20; SCON=0x50; TH1=0xcc; TR1=1; }
Remember that x+0x30 will only yield an ASCII digit code (ie, '0' to '9') if the value of x is between 0 and 9.
If x has any other values, you will see garbage!
How are you checking that you have valid values in the range 0..9?
The code you posted is illegible because you didn't follow the instructions for posting code. :-( Please read them, and re-post your code accordingly: http://www.keil.com/forum/tips.asp
"actually the pointer is not the question over here."
But do you understand why your example with the pointer was incorrect, and could not possibly have worked?
Hi thanks for your reply. actually the pointer is not the question over here. even if i try to use any other variable other than pointers and try to display the values i am getting garbage values on the screen.
how about,
unsigned int r = *p; serial_num(r+0x30);
Take a careful look at the expression (*p+0x30) Ask yourself: what is the 1st operand of the '+' operator here? ie, are you adding 0x30 to the pointer, or to the pointed-to value? In fact, (*p+0x30) is equivalent to p[0x30] - which is, presumably, not what you want. Presumably, what you want is (*p)+0x30 ? See: c-faq.com/.../unopprec2.html BTW: using 0x30 as a Magic Number is poor style, since what you actually mean is "the ASCII code for the character '0'". Therefore, it would be clearer to write (*p)+'0' - and still put an explanatory comment.
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