ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 259

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Latching of Fuses
Signature Bytes
Calibration Byte
Parallel Programming
Parameters, Pin
Mapping, and
Commands
Signal Names
2570A–AVR–09/04
The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are
locked if Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the
Lock bits.
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.
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 ATmega325/3250/645/6450 the signature bytes are:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x95/0x96 (indicates Flash memory,refer to “Part Number” on page 217).
3. 0x002: 0x03/0x04 (indicates device, refer to “Part Number” on page 217).
The ATmega325/3250/645/6450 has a byte calibration value for the internal RC Oscilla-
tor. 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 cor-
rect frequency of the calibrated RC Oscillator.
This section describes how to parallel program and verify Flash Program memory,
E E P R O M D a t a m e m o r y , M e m o r y L o c k b i t s , a n d F u s e b i t s i n t h e
ATmega325/3250/645/6450. Pulses are assumed to be at least 250ns unless otherwise
noted.
In this section, some pins of the ATmega325/3250/645/6450 are referenced by signal
names describing their functionality during parallel programming, see Figure 111 and
Table 112. 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 posi-
tive pulse. The bit coding is shown in Table 114.
When pulsing WR or OE, the command loaded determines the action executed. The dif-
ferent Commands are shown in Table 115.
ATmega325/3250/645/6450
259