Datasheet

29.7 Parallel Programming
29.7.1 Enter Programming Mode
The following algorithm puts the device in Parallel Programming mode:
1. Apply 4.5 - 5.5V between V
CC
and GND, and wait at least 100µs.
2. Set RESET to “0” and toggle XTAL1 at least 6 times
3. Set the Prog_enable pins listed in table Pin Values Used to Enter Programming Mode to “0000” and
wait at least 100ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100ns after +12V has been
applied to RESET, will cause the device to fail entering Programming mode.
Note, if the RESET pin is disabled by programming the RSTDISBL Fuse, it may not be possible to follow
the proposed algorithm above. The same may apply when External Crystal or External RC configuration
is selected because it is not possible to apply qualified XTAL1 pulses. In such cases, the following
algorithm should be followed:
1. Set Prog_enable pins listed in table Pin Values Used to Enter Programming Mode to “0000”.
2. Apply 4.5 - 5.5V between V
CC
and GND simultaneously as 11.5 - 12.5V is applied to RESET.
3. Wait 100ns.
4. Re-program the fuses to ensure that External Clock is selected as clock source (CKSEL3:0 =
0’b0000) and RESET pin is activated (RSTDISBL unprogrammed). If Lock Bits are programmed, a
chip erase command must be executed before changing the fuses.
5. Exit Programming mode by power the device down or by bringing RESET pin to 0’b0.
6. Entering Programming mode with the original algorithm, as described above.
29.7.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command needs only be loaded once when writing or reading multiple memory locations.
• Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the EESAVE
Fuse is programmed) and Flash after a Chip Erase.
• Address high byte needs only be loaded before programming or reading a new 256 word window in
Flash or 256byte EEPROM. This consideration also applies to Signature bytes reading.
29.7.3 Chip Erase
The Chip Erase will erase the Flash, the SRAM and the EEPROM memories plus Lock bits. The Lock bits
are not reset until the program memory has been completely erased. The Fuse bits are not changed. A
Chip Erase must be performed before the Flash and/or EEPROM are reprogrammed.
Note: The EEPROM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”:
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
AVR 8-Bit Microcontroller
MEMPROG- Memory Programming
© 2017 Microchip Technology Inc.
Datasheet Complete
40001974A-page 294