Datasheet

231
7728G–AVR–06/10
ATtiny87/ATtiny167
21.7 Parallel Programming
21.7.1 Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between Vcc and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 21-10 on page 230 to “0000
b
” 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 programming
mode.
5. Wait at least 50 µs before sending a new command.
21.7.2 Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For effi-
cient 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.
21.7.3 Chip Erase
The Chip Erase will erase the Flash and EEPROM
(Note:)
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 EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.
Load Command “Chip Erase”
1. Set XA1, XA0 to “1,0
”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000
b
”. 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.