Datasheet

157
8024A–AVR–04/08
ATmega8HVA/16HVA
27.8 High-voltage Serial Programming Algorithm
To program and verify the ATmega8HVA/16HVA in the High-voltage Serial Programming mode,
the following sequence is recommended (See instruction formats in Table 27-14):
27.8.1 Enter High-voltage Serial Programming Mode
The following algorithm puts the device in Serial (High-voltage) Programming mode:
1. Set Prog_enable pins listed in Table 27-12 on page 156 to “0000”, RESET pin to 0V and
V
CC
to 0V.
2. Apply 3.0 - 3.5V between V
CC
and GND. Ensure that V
CC
reaches at least 1.8V within the
next 20 µs.
3. Wait 20 - 60 µs, and apply V
HRST
- 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least t
HVRST
after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Release Prog_enable[1] pin to avoid drive contention on the Prog_enable[1]/SDO pin.
6. Wait at least 300 µs before giving any serial instructions on SDI/SII.
If the rise time of the V
CC
is unable to fulfill the requirements listed above, the following alterna-
tive algorithm can be used.
1. Set Prog_enable pins listed in Table 27-12 on page 156 to “0000”, RESET pin to 0V and
V
CC
to 0V.
2. Apply 3.0 - 3.5V between V
CC
and GND.
3. Monitor V
CC
, and as soon as V
CC
reaches 0.9 - 1.1V, apply V
HRST
- 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least t
HVRST
after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Release Prog_enable[1] pin to avoid drive contention on the Prog_enable[1]/SDO pin.
6. Wait until V
CC
actually reaches 3.0 - 3.5V before giving any serial instructions on SDI/SII.
27.8.2 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.
Table 27-13. High-voltage Reset Characteristics
Supply Voltage RESET Pin High-voltage Threshold
Minimum High-voltage Period for
Latching Prog_enable
V
CC
V
HVRST
t
HVRST
3.0V 11.5V 10 µs
3.5V 11.5V 10 µs