Datasheet

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