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; }
I notice quite a few changes in the second version of code. This one is quite interesting:
unsigned int xdata count _at_ 0xA005, *p _at_ 0xA007 , x _at_ 0xA009;
changes to:
unsigned int xdata count _at_ 0xA005, *p _at_ 0xA007 , x _at_ 0xA00A;
however you no longer use 'p', instead you dereference an uninitialised pointer 'pt'.
It also looks as though you have some sort of unusual xdata addressing scheme going on where it would appear (although I'm guessing) that you try to write to xdata while it is in 'read mode'. Would you care to elaborate a little on your RAM interface?
What are you tring to do? Is there a reason you do not want the compiler to place the variables
Are you sure everythig fits? how big is a pointer unsigned int xdata *p _at_ 0xA007 put a generic pointer (3 bytes) in to Xdata at address 0xA007. It points to nothing. _at_ is usually used to get to memory mapped I/O
A memory mapped pointer must be some interesting HW.
"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; "
This was the code posted, and Raghu Ravi quoted the problem: "since 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."
working to see what was the output ..
When we compile a program, does it give the desired output? Yes - wow, attempt right, no - debug, and find what problem,
beginners as told put a printf and see what values are being to variables, any mistake in that, am afraid not, if so, pardon, no special intention, once we make up mind to start writing a program with an aim, is nt it run to completion,
New to programming, just seeing how the program works,
"unsigned int xdata count _at_ 0xA005, *p _at_ 0xA007 , x _at_ 0xA009;" generated a warning L6: Xdata space memory overlap, From: A009h To: A009h
make it A00A, and warninig disappeared, though output is the same in both cases.6.
beginners as told put a printf why on earth overload memory with that monster? This particular 'problem' sounds like something that can be sorted out in the simulator.
Erik