ATmega325P datasheet(274/364 Pages) ATMEL

274 / 364 page

274

8023F–AVR–07/09

ATmega325P/3250P

25.2.1

Latching of Fuses

The fuse values are latched when the device enters programming mode and changes of the

fuse values will have no effect until the part leaves Programming mode. This does not apply to

the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on

Power-up in Normal mode.

25.3

Signature Bytes

All Atmel microcontrollers have a three-byte signature code which identifies the device. This

code can be read in both serial and parallel mode, also when the device is locked. The three

bytes reside in a separate address space. For the ATmega325P/3250P the signature bytes are

given in Table 25-6

25.4

Calibration Byte

The ATmega325P/3250P has a byte calibration value for the internal RC Oscillator. This byte

resides in the high byte of address 0x000 in the signature address space. During reset, this byte

is automatically written into the OSCCAL Register to ensure correct frequency of the calibrated

RC Oscillator.

25.5

Parallel Programming Parameters, Pin Mapping, and Commands

This section describes how to parallel program and verify Flash Program memory, EEPROM

Data memory, Memory Lock bits, and Fuse bits in the ATmega325P/3250P. Pulses are

assumed to be at least 250ns unless otherwise noted.

25.5.1

Signal Names

In this section, some pins of the ATmega325P/3250P are referenced by signal names describ-

ing their functionality during parallel programming, see Figure 25-1 on page 275 and Table 25-7

on page 275. Pins not described in the following table are referenced by pin names.

The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.

The bit coding is shown in Table 25-9 on page 276.

When pulsing WR or OE, the command loaded determines the action executed. The different

Commands are shown in Table 25-10 on page 276.

Table 25-6.

Device and JTAG ID

Parts

Signature Bytes Address

JTAG

0x000

0x001

0x002

Part Number

Manufacture ID

ATmega325P

0x1E

0x95

0x0D

950D

0x1F

ATmega3250P

0x1E

0x95

0x0E

950E

0x1F

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