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18F #ROM EEPROM

 
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rhaguiuda



Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil

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18F #ROM EEPROM
PostPosted: Wed Mar 04, 2009 5:29 am     Reply with quote
Hi

I was using a program with PIC16F876. This program has at start the directive:

Code:
#ROM 0x2100 = {1,2,3,4}


So, when this program was writed it worked well, and initial EEPROM values were right.

Then using the same program, I migrated to PIC18F2420. I'v changed the #ROM to:

Code:
#ROM 0xF00000 = {1,2,3,4}


And something strang happend. At EEPROM looks like:

Adress 0: 1
Adress 1: 0
Adress 2: 2
Adress 3: 0
Adress 4: 3
Adress 5: 0
Adress 6: 4
Adress 7: 0

It appears to using 2 bytes for each number I write. How this could happen?
I was expecting the same behavior that PIC16F have.

CCS PCH C Compiler, Version 4.084
Using CCS C Plugin for MPLAB and Programming in MPLAB.
Thanks!
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FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Wed Mar 04, 2009 6:18 am     Reply with quote
Quote:
How this could happen?

The behaviour is by design. PCM has 14-Bit ROM and word addressing, so 8-Bit data is placed to consecutive ROM words. PCH has 16-Bit ROM and byte addressing. #ROM data is interpreted as int16 by default, so you get zero high bytes. By specifying #ROM int8 option, you can place byte data to consecutive byte addresses.
rhaguiuda



Joined: 05 Sep 2007
Posts: 46
Location: Londrina - Brazil

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PostPosted: Wed Mar 04, 2009 6:33 am     Reply with quote
Thanks FvM

It works!
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Give a man a fish and you'll feed him for a day. Teach a man to fish, and you'll feed him for a lifetime.
mpaulao



Joined: 30 Aug 2011
Posts: 1
Location: Brasil

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Use #rom int 8 option
PostPosted: Fri Jan 06, 2012 5:31 pm     Reply with quote
Hello FvM!

I want information about #rom directive.
Your response save me!

Thank you!

Marcos Paulão
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