Signature Bytes

Calibration Byte

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 ATmega128 the signature bytes are:

1.$000: $1E (indicates manufactured by Atmel)

2.$001: $97 (indicates 128KB Flash memory)

3.$002: $02 (indicates ATmega128 device when $001 is $97)

The ATmega128 stores four different calibration values for the internal RC Oscillator. These bytes resides in the signature row high byte of the addresses 0x000, 0x0001, 0x0002, and 0x0003 for 1, 2, 4, and 8 MHz respectively. During Reset, the 1 MHz value is automatically loaded into the OSCCAL Register. If other frequencies are used, the calibration value has to be loaded manually, see “Oscillator Calibration Register – OSCCAL” on page 39 for details.

Parallel Programming

Parameters, Pin

Mapping, and

Commands

Signal Names

This section describes how to parallel program and verify Flash Program memory, EEPROM Data memory, Memory Lock bits, and Fuse bits in the ATmega128. Pulses are assumed to be at least 250 ns unless otherwise noted.

In this section, some pins of the ATmega128 are referenced by signal names describing their functionality during parallel programming, see Figure 135 and Table 120. 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 122.

When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 123.

Figure 135. Parallel Programming

XA1 PD6

PAGEL PD7

+12 V RESET

XTAL1

GND