ATmega325P datasheet(277/364 Pages) ATMEL

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277

8023F–AVR–07/09

ATmega325P/3250P

Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been

applied to ensure the Prog_enable Signature has been latched.

Wait at least 300 µs before giving any parallel programming commands.

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.

Set Prog_enable pins listed in Table 25-8 on page 275 to “0000”, RESET pin to 0V and

CC to 0V.

Apply 4.5 - 5.5V between V

CC and GND.

Monitor V

CC, and as soon as VCC reaches 0.9 - 1.1V, apply 11.5 - 12.5V to RESET.

Keep the Prog_enable pins unchanged for at least 10µs after the High-voltage has been

applied to ensure the Prog_enable Signature has been latched.

Wait until V

CC actually reaches 4.5 -5.5V before giving any parallel programming

commands.

Exit Programming mode by power the device down or by bringing RESET pin to 0V.

25.6.2

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.

25.6.3

Chip Erase

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 perfor med before the Flash and/or EEPROM are

reprogrammed.

Note:

1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.

Load Command “Chip Erase”

Set XA1, XA0 to “10”. This enables command loading.

Set BS1 to “0”.

Set DATA to “1000 0000”. This is the command for Chip Erase.

Give XTAL1 a positive pulse. This loads the command.

Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.

Wait until RDY/BSY goes high before loading a new command.

25.6.4

Programming the Flash

The Flash is organized in pages, see Table 25-11 on page 276. When programming the Flash,

the program data is latched into a page buffer. This allows one page of program data to be pro-

grammed simultaneously. The following procedure describes how to program the entire Flash

memory:

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