how to access memory location in embedded c?

hiren.dave@bhuved.com · Aug 8, 2012

hi.

i want to know that how to access memory location in embedded c?

i have 1 register a and i want to store this in memory location 0x501 than how should i defined??

hexreader · Aug 8, 2012

Which C compiler are you using?

Which processor are you using?

What is this "register a"?

Ian Rogers · Aug 8, 2012

In Hi-tech C its...

Code:

volatile unsigned char Portvar @ 0x06;

which equates to

Code:

_Portvar EQU 06h

straight out of the manual..... Absolute variables.....

My question.... Why? In C you can create a pointer to a variable anyway! I've NEVER needed this facility.

WTP Pepper · Aug 8, 2012

e.g.

#define PORT (* (unsigned char *) (0x0501))

PORT=0x33;
x=PORT;
etc etc

hiren.dave@bhuved.com · Aug 9, 2012

hi..

thanks for your reply. How to use pointer to indicate memory locations?
wtp pepper, i used your technique but it doesn't store data.

Ian Rogers · Aug 10, 2012

Create a location..

Code:

char x;

This maybe anywhere in data memory..

Create a pointer...

Code:

char * ptr;

Now you dont need to know where it is..

Point at the variable.

Code:

ptr = &x;

&x; the address of x... x and ptr are now referenced..

Code:

x=5;
*ptr = 5;

You can also create a pointer to a constant..

Code:

const char * cp;
const char inputData[1000] @ 0x900;
cp = &inputData;
// cp is incremented over inputData and used to read values there

(Straight out of the manual...)

Pommie · Aug 10, 2012

I wonder if 0x501 is in data or program memory or even both!!

Mike.

3v0 · Aug 10, 2012

Why you need to do this. All of the SFRs are mapped to correct locations by the processor header files.

We define linker sections to memory ranges, are you trying to get around that ?

Ian Rogers · Aug 10, 2012

3v0 said:
Why you need to do this. All of the SFRs are mapped to correct locations by the processor header files.

We define linker sections to memory ranges, are you trying to get around that ?

Exactly....... As I said, all my years I have never needed this....

WTP Pepper · Aug 10, 2012

3v0 said:
Why you need to do this. All of the SFRs are mapped to correct locations by the processor header files.

We define linker sections to memory ranges, are you trying to get around that ?

Well they weren't in 1988 when I started using the IAR C compiler for the 68HC11.

WTP Pepper · Aug 10, 2012

hiren.dave@bhuved.com said:
hi..

thanks for your reply. How to use pointer to indicate memory locations?
wtp pepper, i used your technique but it doesn't store data.

Some registers are write only and do not return the value that was written. They are latches. You are best as said elsewhere keeping a local variable as to what has been written and modifiying that before writing to a port. The example I gave works for writing to a Port and reading from a memory location.

3v0 · Aug 11, 2012

hiren.dave Is an expert at NOT answering questions.

how to access memory location in embedded c?

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