Weird problem with global variable int dat[64]?

arrow · Joined: 17 May 2005 Posts: 213

Hi

I have an accelerometer which outputs in PWM. I use the PIC16F873 to time the pulse duty cycle.
Things work well.

Then I add the following lines at the top of file:

#define EEPROM_SDA PIN_C4
#define EEPROM_SCL PIN_C3

#define EEPROM_SIZE 32000
#define PAGE_SIZE 64
#define NO_EEPROMS 1

#use i2c(master,sda=EEPROM_SDA, scl=EEPROM_SCL)
//--------------------------------
int dat[64];
//====================

Things work fine if I dont include the int dat[64] line.
If I do add it in, the program does not perform as expected.
i.e. initially i get 0x82 output to my RS232 port, and now I get
a mixture of 0x82, and 0X56 data. The 0x56 should not be there.
So somehow things have changed, when I only include some definitions,
and space allocation. (I have not changed the program, and do not
do anything with the dat variable).

Can someone please tell me what I am doing wrong?

Thank you
arrow

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

Sounds like a banks switching problem. By adding the new array of data your memory map has changed. You didn't mention your compiler version but some bugs related to bank switching have been solved in the past.

PIC processors are more memory efficient when the large global variables are placed at the end of memory. Check your symbol table (*.sym file) for variables crossing bank borders. Try moving the array to another bank (#locate directive).

Guest · Posted: Thu Jun 23, 2005 7:18 am

Hi Ckielstra

My compiler version is:

2.686

I dont seem to have the #locate directive.
Can I use some other directive/ command? to specify the exact position in memory?
and if so, can you please give me an example?

Thank you very much
arrow

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

With your version, you can use a #byte statement after the
array declaration to set the address of the array at the
beginning of RAM Bank 3. See the test program below.

After compiling, the the .SYM file has this entry:

Guest · Posted: Fri Jun 24, 2005 2:00 am

Hi PCM programmer

I hvae tried doing what you suggest.
I had to use

#byte dat = 0x20

to get even the first part of the code to work.

When i was accessing the data (first writting and then reading),
the data came out in a mess.

Can you please tell me what I am doing wrong?

Thank you
arrow

My code snippet is:

#fuses LP,PROTECT,NOWDT,NOBROWNOUT

#use delay(clock=4000000)
#use rs232(baud=19200, xmit=PIN_C6, rcv=PIN_C7,ERRORS)

#define ACCELEROMETER_X PIN_C2

#define EEPROM_SDA PIN_C4
#define EEPROM_SCL PIN_C3

#define EEPROM_SIZE 32000
#define PAGE_SIZE 32
#define NO_EEPROMS 1

#use i2c(master,sda=EEPROM_SDA, scl=EEPROM_SCL, NOFORCE_SW )

int dat[PAGE_SIZE];
#byte dat = 0x20

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

I was just answering that specific question. I didn't expect it to solve
any of your problems.