Datasheet

159
2586D–AVR–02/06
ATtiny25/45/85
23.8 High-voltage Serial Programming Algorithm
To program and verify the ATtiny25/45/85 in the High-voltage Serial Programming mode, the fol-
lowing sequence is recommended (See instruction formats in Table 23-15):
23.8.1 Enter High-voltage Serial Programming Mode
The following algorithm puts the device in High-voltage Serial Programming mode:
1. Set Prog_enable pins listed in Table 23-13 to “000”, RESET pin and V
CC
to 0V.
2. Apply 4.5 - 5.5V 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 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO
pin.
6. Wait at least 300 µs before giving any serial instructions on SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
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 23-13 to “000”, RESET pin and V
CC
to 0V.
2. Apply 4.5 - 5.5V between V
CC
and GND.
3. Monitor V
CC
, and as soon as V
CC
reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 µs after the High-voltage has been
applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable[2] pin to avoid drive contention on the Prog_enable[2]/SDO
pin.
6. Wait until V
CC
actually reaches 4.5 - 5.5V before giving any serial instructions on SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
23.8.2 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.
Table 23-14. 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
4.5V 11.5V 100 ns
5.5V 11.5V 100 ns