Signature Bytes

Calibration Byte

Parallel Programming

Parameters, Pin

Mapping, and

Commands

Signal Names

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 has a byte calibration value for the internal RC Oscillator. This byte resides in the high byte of address $000 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.

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 121. 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 123.

When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 124.

Figure 135. Parallel Programming

+5V

RDY/BSY PD1

VCC

OE PD2

PB7 - PB0 DATA

WR PD3

BS1 PD4

XA0 PD5

XA1 PD6

PAGEL PD7

+12 V RESET

BS2 PA0

XTAL1

GND

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Table 121. Pin Name Mapping

	Signal Name in
	Programming Mode						Pin Name	I/O	Function
									0: Device is busy programming, 1: Device is ready
	RDY/BSY						PD1	O
									for new command
							PD2	I	Output Enable (Active low)
		OE
							PD3	I	Write Pulse (Active low)
	WR
	BS1						PD4	I	Byte Select 1 (“0” selects low byte, “1” selects high
									byte)
	XA0						PD5	I	XTAL Action Bit 0
	XA1						PD6	I	XTAL Action Bit 1
	PAGEL						PD7	I	Program Memory and EEPROM data Page Load
	BS2						PA0	I	Byte Select 2 (“0” selects low byte, “1” selects 2’nd
									high byte)
	DATA						PB7-0	I/O	Bidirectional Data bus (Output when		is low)
										OE

Table 122. Pin Values Used to Enter Programming Mode

Pin	Symbol	Value
PAGEL	Prog_enable[3]	0
XA1	Prog_enable[2]	0
XA0	Prog_enable[1]	0
BS1	Prog_enable[0]	0

Table 123. XA1 and XA0 Coding

	XA1	XA0	Action when XTAL1 is Pulsed
	0	0	Load Flash or EEPROM Address (High or low address byte determined by
			BS1)
	0	1	Load Data (High or Low data byte for Flash determined by BS1)
	1	0	Load Command
	1	1	No Action, Idle

Table 124. Command Byte Bit Coding

Command Byte	Command Executed
1000 0000	Chip Erase
0100 0000	Write Fuse Bits
0010 0000	Write Lock Bits
0001 0000	Write Flash
0001 0001	Write EEPROM

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