Datasheet

304
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
27.7 Parallel programming
27.7.1 Enter Programming mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between V
CC
and GND.
2. Set RESET
to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 27-11 on page 303 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.
5. Wait at least 50µs before sending a new command.
27.7.2 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 256 byte EEPROM. This consideration also applies to Signature bytes
reading
27.7.3 Chip Erase
The Chip Erase will erase the Flash and EEPROM
(1)
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: 1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
Table 27-13. Command byte bit encoding.
Command byte Command executed
1000 0000 Chip Erase
0100 0000 Write Fuse bits
0010 0000 Write Lock bits
0001 0000 Write Flash
0001 0001 Write EEPROM
0000 1000 Read Signature Bytes and Calibration byte
0000 0100 Read Fuse and Lock bits
0000 0010 Read Flash
0000 0011 Read EEPROM