word address or byte address?

[santosh.manicka]

I am using a PIC18F6722 and PCW compiler.
In the function, write_program_memory( address, dataptr, count );
is 'address' a word-address or a byte-address?

I know it's an int32 and table read/writes between program memory and data memory happen in bytes, but they don't necessarily imply that the above function uses a word-address.

Gurus, please respond!

[PCM programmer]

The CCS manual makes it clear that the function writes bytes.

[santosh.manicka]

Well, assume that 'address' is a word-address. For instance,

address = 0x0000; //address points to the 0th byte
int8 data = 1; //&data points to 1 byte
write_program_memory(address, &data, 1);

address++; // Now, address points to the 2nd byte because it points to a wrd
write_program_memory(address, &data, 1);

Therefore, the 0th byte and the 2nd byte contain the value one but the 1st byte has been skipped.

Since the above is also possible, it does not seem obvious to me that 'address' has to be a byte-address.

[SherpaDoug]

The sure-fire way to tell is to write a trivial program and look at the assembly code it creates. That will answer all questions.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[gribas]

I think you're mixing things up. Do you understand the difference between:

[santosh.manicka]

I had mentioned the data type in my first post...may be I didn't emphasize enough on that.

In my example, address in int32.
So, address++ will increment it by 1, I understand. The function where I am using this variable is write_program_memory which will write into the program memory and NOT the RAM.

So, if the processor's addressing mode is word rather than byte, then the next address will point to the next word...OR may be the compiler sees it as a byte-address and handles the word-addressing mode on its own with the processor. That's what I want to clarify.

[gribas]

Sorry, I misunderstood your question.

You're right, the PC is always even, which means it can never point to an address like 0x0001. But that doesn't imply that word addressing is used for all access to the program memory.

According to my datasheet (18f4525), the program memory is addressed in bytes and you can read and write wherever you see fit. You have to write in chunks of 64 bytes but that's another issue...

So, the PIC is capable and the docs state that the compiler is capable of byte addressing. I've never used that function so I cannot vouch for it.

Do as SherpaDoug said and you'll have your unassailable answer =). Just comment the line #nolist in your "18F6722.h" so you can see all the code for the function.

hope it helps,

[santosh.manicka]

Thank you for the suggestions. I wrote the following piece and concluded that successive addresses(int32 values) refer to the successive bytes and not words.

[Ttelmah]

I agree the manual is not exactly 'explicit' about this.
It is clear in the function that give 16bit writes - write_program_eeprom, where the manual says that when writing these 16bit values, the LSB of the address, must always be '0', which tells you that the address is in bytes, and because you are writing whole words, you can only access the even addresses.

Best Wishes