Specifications

Chapter 2 - Microcontroller PIC16F84

0=writing disallowed

bit 3 WRERR (Write EEPROM Error Flag ) Error during writing to EEPROM

This bit was set only in cases when writing to EEPROM had been interrupted by a reset signal or

by running out of time in watchdog timer (if it's activated).

1=error occured

0=error did not occur

bit 4 EEIF (EEPROM Write Operation Interrupt Flag bit) Bit used to inform that writing data to

EEPROM has ended.

When writing has terminated, this bit would be set automatically. Programmer must clear EEIF bit

in his program in order to detect new termination of writing.

1=writing terminated

0=writing not terminated yet, or has not started

Reading from EEPROM Memory

Setting the RD bit initializes transfer of data from address found in EEADR register to EEDATA

EEDATA register can already be used further in the next instruction.

Sample of the part of a program which reads data in EEPROM, could look something like the

following:

After the last program instruction, contents from an EEPROM address zero can be found in working

Writing to EEPROM Memory

In order to write data to EEPROM location, programmer must first write address to EEADR register

and data to EEDATA register. Only then is it useful to set WR bit which sets the whole action in

motion. WR bit will be reset, and EEIF bit set following a writing what may be used in processing

interrupts. Values 55h and AAh are the first and the second key whose disallow for accidental

writing to EEPROM to occur. These two values are written to EECON2 which serves only that

purpose, to receive these two values and thus prevent any accidental writing to EEPROM memory.

Program lines marked as 1, 2, 3, and 4 must be executed in that order in even time intervals.

Therefore, it is very important to turn off interrupts which could change the timing needed for

executing instructions. After writing, interrupts can be enabled again .

Example of the part of a program which writes data 0xEE to first location in EEPROM memory

could look something like the following:

http://www.mikroelektronika.co.yu/english/product/books/PICbook/2_09Poglavlje.htm (2 of 3) [4/2/2003 16:18:00]