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ATmega8A [DATASHEET]
8159E–AVR–02/2013
25.7
Parallel Programming
25.7.1
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 100s.
2.
Set RESET to “0” and toggle XTAL1 at least 6 times
3.
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 pro-
posed 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.
2.
Apply 4.5 - 5.5V between V
CC and GND simultaneously as 11.5 - 12.5V is applied to RESET.
3.
Wait 100 ns.
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 com-
mand 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.
25.7.2
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.
25.7.3
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 the EEPROM are reprogrammed.
Note:
1. The EEPRPOM memory is preserved during chip erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
0000 0100
Read Fuse and Lock Bits
0000 0010
Read Flash
0000 0011
Read EEPROM
Table 25-10. Command Byte Bit Coding
Command Byte
Command Executed