The following algorithm puts the device
in Parallel Programming mode:
- 1.Apply 4.5 - 5.5V between VCC 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
VCC 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.