Porky code on 18F2520 ... need more ROM

evsource · Joined: 21 Nov 2006 Posts: 129

I'm sure everyone is tired of hearing about out-of-ROM errors. I hit the ROM barrier with the 16F876, so I went to the 18F2520. Well, the code has grown and grown, and now I'm out of space again.

I'm doubtful, but is there any pin-for-pin replacement for the 18F2520 that has more space? I'm sure I could optimize a bit and use up less space, but I'm looking for the quick and easy solution Smile

Thanks in advance.

Storic · Joined: 03 Dec 2005 Posts: 182 Location: Australia SA

try the 18f2620 (double the ROM of the 2520)
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010284

I assume it is pin compatible, I know the 4520 and the 4620 are (44 pin version of the chip you are referring to).

Idea

Check the data sheet
_________________
What has been learnt if you make the same mistake? Wink

evsource · Joined: 21 Nov 2006 Posts: 129

silelis · Posted: Thu Jun 21, 2007 7:55 am

Few day ago I had problem with ROM so I changed PIC16f77 to PIC18f4620 and it's working without any problem.

But I've got question: Is there any posibility to read PIC program form external ROM location?

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

What do you mean by external ROM.

Do you have a chip part number?

silelis · Posted: Tue Sep 25, 2007 2:08 am

I mean is it possible to read program on the flow from for example EEPROM, memory card or some other kind of memory?

ELCouz · Joined: 18 Jul 2007 Posts: 427 Location: Montreal,Quebec

Basic stamp does it (using a pic with a bootloader inside ,,, then read the program from a eeprom chip)... so its possible to do it Wink

so you might check for a pic bootloader that read a program from a eeprom.

libor · Joined: 14 Dec 2004 Posts: 288 Location: Hungary

Yes. Some high end (18F8xxx) chips have parallel external memory interface. They can use external memory (EPROMs, Flash, or even SRAM) up to 2Mbytes both for running code from and/or data.
Read the AN869 - External Memory Interfacing Techniques for the PIC18F8XXX.

You can also make your own solution for huge programs: write you own interpreter residing in the main chip and execute your own pseudo-code (optimized for that particular project) from the external memory on the fly.

arunb · Joined: 08 Sep 2003 Posts: 492 Location: India

Hi,

Out of ROM errors could also occur if a function is larger than the page size...you could isolate the function and break it down into smaller pieces...

thanks
arunb

Ttelmah · Guest

There are two different ways to do this. The first is a chip that supports using an external memory. You can then run 'real' code from this. The second, is to not actually 'run' the code, but use number stored externally, with an interpreter that is running on the main chip. This is what the 'basic STAMP' does. On these the PIC itself, does not execute the external code, but performs relatively high level functions based on a numeric value read from the external chip.
This is obviously slower, but has the advantage that the memory does not have to be directly accessed.

Best Wishes