XDATA variables

You have qualified your question with the title "XDATA variables". Does that mean that if you print a constant or a variable not defined XDATA, you will get the printout you expected?

Per,

I have a lot of other variables declared in XDATA that I can access. I can't access that one in particular.

unsigned char xdata rx_buffer[BUF_SIZE]   _at_ 0x0000;
unsigned char xdata tx_buffer_0[BUF_SIZE] _at_ 0x0101;
unsigned char xdata tx_buffer_1[BUF_SIZE] _at_ 0x0202;
unsigned char xdata com_buffer[COM_SIZE]  _at_ 0x0303;
unsigned char xdata htem_msg[128]         _at_ 0x0354;
unsigned char xdata screen_cmd[10]        _at_ 0x03D5;
float xdata         voltage               _at_ 0x08E2;


unsigned char xdata *p_rx_write   = rx_buffer;
unsigned char xdata *p_rx_read    = rx_buffer;
unsigned char xdata *p_tx_0_write = tx_buffer_0;
unsigned char xdata *p_tx_0_read  = tx_buffer_0;
unsigned char xdata *p_tx_1_write = tx_buffer_1;
unsigned char xdata *p_tx_1_read  = tx_buffer_1;
unsigned char xdata *p_com_write  = com_buffer;

unsigned int xdata counter_5Hz = 0;
unsigned int xdata counter_2Hz = 0;
unsigned int xdata counter_1Hz = 0;

unsigned long xdata ad_cnt    = 0;
char xdata          data_chnl = 0;

int xdata i = 0; j = 0; k = 0;

unsigned int xdata  timer_mask  = 1;
unsigned char xdata timer_state = 0;

All of these are accessible except for voltage.

I think I found the possible cause.

If I keep all XDATA varibles between 0x0000 ~ 0x0400 I can access them.

Here is the question, though. Shouldn't I have access to all 32K of program memory if I don't declare any data flash memory? I'm new to the 8051 development environment so this is a little confusing.

Thanks.

You haven't mentioned what chip you use.

What do you mean by "data flash memory"? The application is normally stored in flash - a special version of PROM that allows quick erase of sectors (or full chip).

But flash memory is not for variables since you can't modify data in flash memory. You have to erase a full sector to be able to write a new value to a variable.

Another thing: The C51 procesors normally separate data and program memory spaces, so a data access instruction can not access program memory, and a code access instruction can not access variable memory. Some C51 processors can have flash memory accessible both ways, to allow storage of either application code or configuration data. But your XDATA variables are expected to be variables, i.e. to bestored in RAM, not in flash.

Have you spent time reading up on the C51 architecture?

Per,

Sorry, I'm using TI's MSC1210Y5. I miss understood the documentation. It states on-chip SRAM is from 0x0000~0x03FF, which makes sense why the variable was in accessible.

Have you spent time reading up on the C51 architecture?

I have very limited resources when it comes to the C51 architecture. I know the net is a great one but I haven't had a chance to filter through the hundreds of pages on the subject. Can you suggest any good ones?

Thanks,
Paul

when it comes to the C51 architecture. ... Can you suggest any good ones?

none better than "the bible"

Erik

here are the links to "the bible"
Chapter 1 - 80C51 Family Architecture:
www.nxp.com/.../80C51_FAM_ARCH_1.pdf

Chapter 2 - 80C51 Family Programmer’s Guide and Instruction Set:
www.nxp.com/.../80C51_FAM_PROG_GUIDE_1.pdf

Chapter 3 - 80C51 Family Hardware Description:
www.nxp.com/.../80C51_FAM_HARDWARE_1.pdf

Is there a reason you are using _at_ instead of letting the compiler place the variables?