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How to create a list on a external EEPROM

 
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Genival
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How to create a list on a external EEPROM
PostPosted: Mon Dec 20, 2004 7:00 am     Reply with quote
Hello people!

I need to implement a user list on a board that use the 16F877 MCU.So, how can I create a sequence of user and how can I know the begin and the end of register of each user into the list.I'm using a 24C256 as external memory, and I need 50 user at least registred.Is it possible?If someone have some example in CCS C I'll appreciate so much for the help!
Thanks all!!!
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Mon Dec 20, 2004 3:48 pm     Reply with quote
I'm sure you want something much more complicated than what I'm
going to tell you, but here goes:

A 24LC256 eeprom has 32768 bytes. If you want to partition it
into at least 50 blocks of user data, then divide 32KB by 50:
Code:

32768
------- = 655.36
 50


So you could allocate 655 bytes per user. But, it's more convenient
to use a binary number for the record size, so let's round it down to 512
bytes per user.

This program will convert a user number from 0 to 49 into a EEPROM
address. You could actually have user numbers from 0 to 63.

Code:
#include <16F877.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

#define get_record_address(x)  (x << 9)

void main()
{
int8 i;
int16 record_address;

// Display the eeprom address for user numbers from 0 to 49.
for(i = 0; i < 50; i++)
   {   
    record_address = get_record_address((int16)i);
    printf("User: %u  record address: %lx \n\r", i, record_address);
   }

while(1);
}
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