Datasheet
245
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
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.
25.3.1 ATmega48 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x92 (indicates 4KB flash memory).
3. 0x002: 0x05 (indicates Atmel ATmega48 device when 0x001 is 0x92).
25.3.2 ATmega88 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x93 (indicates 8KB flash memory).
3. 0x002: 0x0A (indicates ATmega88 device when 0x001 is 0x93).
25.3.3 ATmega168 Signature Bytes
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB flash memory).
3. 0x002: 0x06 (indicates Atmel ATmega168 device when 0x001 is 0x94).
25.4 Calibration Byte
The Atmel ATmega48/88/168 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 Atmel ATmega48/88/168. Pulses are assumed to be at least 250ns unless otherwise noted.
25.5.1 Signal Names
In this section, some pins of the ATmega48/88/168 are referenced by signal names describing their functionality during
parallel programming, see Figure 25-1 on page 246 and Table 25-8 on page 246. 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 25-10 on page 246.
When pulsing WR
or OE, the command loaded determines the action executed. The different Commands are shown in
Table 25-11 on page 247.