EPRead

Syntax:

    EPRead location, store

Command Availability:

Available on all Microchip PIC and Atmel AVR microcontrollers with EEPROM data memory.

Explanation:

EPRead reads a byte from the EEPROM data storage built into many microcontroller chips. location is the address to read from, and its valid range depends on the chip in use. store is the variable that receives the value once it has been read.

Note: Do not read 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.

Example:

    'Program to turn a light on and off
    'Will remember the last status

    #chip tiny2313, 1
    #define Button PORTB.0
    #define Light PORTB.1

    Dir Button In
    Dir Light Out

    'Load saved status
    EPRead 0, LightStatus          ' <<< the EPRead instruction

    If LightStatus = 0 Then
      Set Light Off
    Else
      Set Light On
    End If

    Do
      'Wait for the button to be pressed
      Wait While Button = On
      Wait While Button = Off
      'Toggle value, record
      LightStatus = !LightStatus
      EPWrite 0, LightStatus

      'Update light
      If LightStatus = 0 Then
        Set Light Off
      Else
        Set Light On
      End If
    Loop

Key line: EPRead 0, LightStatus — reads the byte stored at EEPROM address 0 back into LightStatus when the chip powers up, so the light remembers whatever state it was last left in.

See Also:

  • EPWrite — writing the value this page reads back
  • Dir — setting the button and light pin directions, as used above
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