ATmega8535(L)

Table 99. Fuse Low Byte

Fuse Low Byte	Bit no	Description	Default Value
BODLEVEL	7	Brown out detector trigger	1	(unprogrammed)
		level
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. See Table 10 on page 28 for details.

2.The default setting of CKSEL3..0 results in internal RC Oscillator @ 1 MHz. See Table 2 on page 23 for details.

The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if Lock bit 1 (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

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 ATmega8535 the signature bytes are:

1.0x000: 0x1E (indicates manufactured by Atmel)

2.0x001: 0x93 (indicates 8 KB Flash memory)

3.0x002: 0x08 (indicates ATmega8535 device when 0x001 is 0x93)

The ATmega8535 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 28 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 ATmega8535. Pulses are assumed to be at least 250 ns unless otherwise noted.

In this section, some pins of the ATmega8535 are referenced by signal names describing their functionality during parallel programming, see Figure 115 and Table 100. 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 102.

When pulsing WR or OE, the command loaded determines the action executed. The different Commands are shown in Table 103.

Figure 115. Parallel Programming

+5V

RDY/BSY

PD1

VCC

OE

PD2

AVCC

WR

PD3

DATA

PB7 - PB0

BS1

PD4

XA0 PD5

XA1 PD6

PAGEL PD7

+12 V RESET

BS2 PA0

XTAL1

GND

Table 100. 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	Bi-directional Data bus (Output when
									OE is low)

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ATmega8535(L)

Table 101. 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 102. 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 103. 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

Table 104.	No. of Words in a Page and no. of Pages in the Flash
Flash Size		Page Size	PCWORD	No. of Pages	PCPAGE	PCMSB
4K words (8K bytes)		32 words	PC[4:0]	128	PC[11:5]	11
Table 105.	No. of Words in a Page and no. of Pages in the EEPROM
EEPROM Size		Page Size	PCWORD	No. of Pages	PCPAGE	EEAMSB
512 bytes		4 bytes	EEA[1:0]	128	EEA[8:2]	8

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