Syntax:
EPWrite location, data
Command Availability:
Available on all Microchip PIC and Atmel AVR microcontrollers with EEPROM data memory.
Explanation:
EPWrite writes a byte to the EEPROM data storage, so it can be read back later by a PC programmer or by the EPRead command. location is the address to write to, and its valid range depends on the chip in use. data is the value to write, and can be a literal or a variable.
Note: Do not write past the end of the chip’s physical EEPROM. If the EEPROM is 256 bytes, location must stay within 0 to 255; if it is 512 bytes, location must stay within 0 to 511 and should be a Word variable rather than a Byte.
Note: EEPROM has a limited write endurance — typically somewhere between 100,000 and 1,000,000 write cycles per location before it may start to fail, depending on the specific chip (check the datasheet for the exact figure). This is rarely a concern for settings written once at power-up, but a loop that writes the same EEPROM location on every pass, such as a data logger, can wear it out in hours or days. Spread frequent writes across multiple locations (wear levelling) if the data does not need to survive at one fixed address.
Example:
#chip 16F819, 8
'Set the input pin direction
Dir PORTA.0 In
'Loop to take readings until the EEPROM is full
For CurrentAddress = 0 to 255
'Take a reading and log it
EPWrite CurrentAddress, ReadAD(AN0) ' <<< the EPWrite instruction
'Wait 10 minutes before getting another reading
Wait 10 min
NextKey line: EPWrite CurrentAddress, ReadAD(AN0) — logs one ADC reading to a different EEPROM address on each pass of the loop, which is exactly the kind of wear-levelling
this page’s endurance note recommends.
See Also:
- EPRead — reading back the value this page writes
- Creating EEProm data from a Lookup Table — pre-loading EEPROM with fixed data at compile time
- ReadAD — reading the sensor value logged in the example above
