How to store a HEX file in rom space of 18F?

FFT · Joined: 07 Jul 2010 Posts: 92

Hi All,

I use PIC18F4520 and I want to store a HEX file in the rom space of the PIC.
PIC's rom has enough free space but I don't know the structure of the rom. If it is like eeprom, I think it is possible to do what I want using write_program_memory command.

Is this possible? Can I write the hex file as below in the rom space and when is needed I should read it to send to another pic?

I want to back-up a .hex file (as txt file) which will be sent thru rs232 and then I want to send it again.

Example hex:

bkamen · Posted: Tue Sep 07, 2010 2:49 pm

Yes you can.

You would use the command write_program_memory just as you describe.
Make sure to read the device's datasheet for specifics as PIC's have different needs when writing to program FLASH. There's also RULES on writing to FLASH as well as the ENDURANCE (that's a keyword) of each flash cell (bit).

You will probably want to plan for how much space you need.. and remember that you could save the HEX to that space as binary or text. Each char is 1 byte. This will include the non-hexadecimal chars like the ':' and CR/LF's.

Those take up space.. so when you LOOK with your eyes at the file, keep in mind there's at LEAST 2 bytes you aren't seeing.

So with that.

Have fun. :D
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

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

Even easier, buy a product that does what you want to do. The Microchip PicKit 2 and 3 come with an included software module called Programmer-To-Go that allows you to use the PicKit as a standalone programmer without the use of a PC. The only difference with your solution is that the target is programmed over the ICD connector instead of over RS232. The PicKit 3 is available for US$45.

CCS sells the Load-n-Go handheld programmer for US$199.

Searching the web you can find more products and hobby projects for the same goal.

bkamen · Posted: Tue Sep 07, 2010 3:03 pm

FFT · Joined: 07 Jul 2010 Posts: 92

@bkamen,
I want to save the hex file as a text (ascii) which means a hex number is 2 bytes. I'll send every every row of the hex file to the pic and it'll write the row to the backup space.

For example If I have 50% free space in rom and I send the same hex of the pic via rs232 to backup space I can't store the hex there (in 50% free space), because the hex is in ascii and it is 2 times bigger, right?

How many bytes I can write in a row (address) of the rom space?

@ckielstra, thanks but I don't wanna make a standalone programmer. I have one.

Now I'll download the datasheet and will take a look.

bkamen · Posted: Tue Sep 07, 2010 4:07 pm

FFT · Joined: 07 Jul 2010 Posts: 92

Hi,

I can't use another pic and I don't have external memory chip.

In datasheet of 18F4520 is written that at a time can be written 32 bytes and can be erased 64 bytes. But how can I understand how many empty rows (addresses) are there?

Maybe I can receive a row of the hex file and delete ":" and checksum bytes, then convert the asciis in hex

for example this row :
:100130003F0156702B5E712B722B732146013421C7

can be converted to :
100130003F0156702B5E712B722B732146013421
and they will be written as hexadecimal using atoi() function,
they are 20 bytes in the example.

But I don't know will I have enough empty rows?

Actually my question is not changed, it is how to store a hex file in the rom space? Of course it should take minimum space.

Or
I can compress every line (row) in the hex file and write them in rom and then decompress and if it is needed reconstruct the row and send it. But I should have a compressing algorithm...

What you recommend?

bkamen · Posted: Tue Sep 07, 2010 8:12 pm

Think about it this way:

You want to use the PIC18F4520.

It has 32768bytes of program memory.

You say your application takes up 1/2 of that.

That leaves you 16384bytes of space left to hold your program copy.

if you took every byte of *program code* in your hex file and saved it to program memory, it would then take up the other half.

The problem is: the HEX file contains more stuff besides just the program code. There's also the config registers which the 4520 has 11. (with jumps in addressing that need to be identified in the hex file)

So it sounds to me like you need to come up with a compression algorithm to cramp on space to store that .HEX file.

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

FFT · Joined: 07 Jul 2010 Posts: 92

Thanks. I know these ideas. I just wanna learn the rom space structure.

if this is the address row and if an address row can contain 64 bytes

FFT · Joined: 07 Jul 2010 Posts: 92

Any help?

Is that correct my previous post?

bkamen · Posted: Thu Sep 09, 2010 2:25 pm

I think you're doing more math than is needed.

The PIC's memory "pages" are just how it's wired to handle the memory.

You don't have to have a line-by-page mapping.

Just look at the raw numbers.

You have X amount of bytes of flash to save stuff.
You have Y chars of HEX file to save.

If (X < Y) {
Get bigger PIC || Add External memory || Compress the image
}
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D

FFT · Joined: 07 Jul 2010 Posts: 92

Thanks, I understood now.

Actually I'm not talking about the pages. In the intel hex link has shown that every text line in the hex file has an address, byte count, checksum, etc..
I'm talking exactly about the address part of a line.
Ex: