ATMEGA8535L_14 Datasheet, PDF (242/321 Pages) ATMEL Corporation – Nonvolatile Program and Data Memories

Parallel Programming
Enter Programming Mode
Considerations for Efficient
Programming
Chip Erase
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 100 µs.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 101 on page 241 to “0000” and wait at
least 100 ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns
after +12V has been applied to RESET, will cause the device to fail entering Pro-
gramming mode.
Note, if External Crystal or External RC configuration is selected, it may not be possible
to apply qualified XTAL1 pulses. In such cases, the following algorithm should be
followed:
1. Set Prog_enable pins listed in Table 101 on page 241 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 100 ns.
4. Re-program the fuses to ensure that External Clock is selected as clock source
(CKSEL3:0 = 0b0000) 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
0b0.
6. Entering Programming mode with the original algorithm, as described above.
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.
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 is reprogrammed.
Note: 1. The EEPRPOM 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.
6. Wait until RDY/BSY goes high before loading a new command.
242 ATmega8535(L)
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