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Store data in ROM

 
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alexz



Joined: 17 Sep 2004
Posts: 133
Location: UK

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Store data in ROM
PostPosted: Fri Feb 11, 2005 6:31 am     Reply with quote
I know there is already a similar topic in the forum, but it didn't really help me.

I am developing a USB mass storage class device using PIC16F877A, compiler version 3.190, MPLAB 7.

I want to store the received data in the ROM memory available in the PIC,
in some chosen locations and retreive the stored data after when needed from these ROM locations.
How can I do it?
How do I choose locations?

Thank you
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Alex
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Fri Feb 11, 2005 6:01 pm     Reply with quote
Quote:

I want to store the received data in the ROM memory available in the
PIC, in some chosen locations and retreive the stored data after when
needed from these ROM locations.
How can I do it?
How do I choose locations?

CCS has an example file for this, called: EX_LOGGER.C

You use an #org statement to preserve an address range in
program memory, so the compiler won't use it.
The #org example in ex_logger.c is overly complex.
In your program, you really probably just need a simple
statement like:
Code:
#org 0x1800, 0x1DFF {}   // Reserve 0x600 words

Then you can use the CCS functions write_program_eeprom()
and read_program_eeprom() to access the memory.

If you're using ICD2 , remember that it loads a "debug executive"
(ie., code) up in high memory in the PIC. For the 16F877A, the
MPLAB vs. 6.42 Help file says the ICD2 uses 0x1F00-0x1FFF.
So don't use that range for your data storage.

Also, the number of times the program memory can be written to
is spec'ed in my 16F877A data sheet at 100K typical, though only 10K
minimum. So if you're going to use it a lot, you should use data eeprom
or external eeprom instead.
alexz



Joined: 17 Sep 2004
Posts: 133
Location: UK

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PostPosted: Mon Feb 14, 2005 3:14 am     Reply with quote
The EEPROM in the PIC16F877A is just 256 bytes unfortunately.
but I need much more.
So how do I choose locations when using #ORG?
Say, if I need to store 1k bytes.
How do I write and read the data?
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Alex
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