ATmega8(L)
		Table 88. Fuse Low Byte
		Fuse Low	Bit
		Byte	No.		Description	Default Value
		BODLEVEL	7		Brown out detector trigger level	1	(unprogrammed)
		BODEN	6		Brown out detector enable	1	(unprogrammed, BOD disabled)
		SUT1	5		Select start-up time	1	(unprogrammed)(1)
		SUT0	4		Select start-up time	0	(programmed)(1)
		CKSEL3	3		Select Clock source	0	(programmed)(2)
		CKSEL2	2		Select Clock source	0	(programmed)(2)
		CKSEL1	1		Select Clock source	0	(programmed)(2)
		CKSEL0	0		Select Clock source	1	(unprogrammed)(2)
		Notes: 1. The default value of SUT1..0 results in maximum start-up time. SeeTable 10 on page
		28 for details.
		2. The default setting of CKSEL3..0 results in internal RC Oscillator @ 1MHz. See
		Table 2 on page 24 for details.
		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.
	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.
	Signature Bytes	All Atmel microcontrollers have a 3-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 ATmega8 the signature bytes are:
		1. 0x000: 0x1E (indicates manufactured by Atmel).
		2. 0x001: 0x93 (indicates 8KB Flash memory).
		3. 0x002: 0x07 (indicates ATmega8 device).
	Calibration Byte	The ATmega8 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 29 for details.

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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 ATmega8. Pulses are assumed to be at least 250 ns unless otherwise noted.

In this section, some pins of the ATmega8 are referenced by signal names describing their functionality during parallel programming, see Figure 104 and Table 89. 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 91.

When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 92.

Figure 104. Parallel Programming

+5V

PD1

RDY/BSY

VCC

OE

PD2

+5V

AVCC

WR

PD3

BS1

PD4

PC[1:0]:PB[5:0]

DATA

XA0

PD5

XA1

PD6

PAGEL

PD7

+12 V

RESET

BS2

PC2

XTAL1

GND

Table 89. Pin Name Mapping

	Signal Name in
	Programming Mode					Pin Name	I/O	Function
								0: Device is busy programming, 1: Device
	RDY/BSY					PD1	O
								is ready for new command
	OE					PD2	I	Output Enable (Active low)
	WR					PD3	I	Write Pulse (Active low)
	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

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ATmega8(L)

Table 89. Pin Name Mapping (Continued)

	Signal Name in
	Programming Mode	Pin Name	I/O	Function
	PAGEL	PD7	I	Program memory and EEPROM Data
				Page Load
	BS2	PC2	I	Byte Select 2 (“0” selects Low byte, “1”
				selects 2’nd High byte)
	DATA	{PC[1:0]: PB[5:0]}	I/O	Bi-directional Data bus (Output when OE is
				low)

Table 90. 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 91. 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 92. 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
0000 1000	Read Signature Bytes and Calibration byte
0000 0100	Read Fuse and Lock Bits
0000 0010	Read Flash
0000 0011	Read EEPROM

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