ATmega8535(L)
Table of Contents	Features.................................................................................................	1
	Pin Configurations................................................................................	2
	Disclaimer .............................................................................................................	2
	Overview................................................................................................	3
	Block Diagram ......................................................................................................	3
	AT90S8535 Compatibility .....................................................................................	4
	Pin Descriptions....................................................................................................	5
	About Code Examples..........................................................................	6
	AVR CPU Core ......................................................................................	6
	Introduction ...........................................................................................................	6
	Architectural Overview ..........................................................................................	6
	ALU – Arithmetic Logic Unit..................................................................................	7
	Status Register .....................................................................................................	8
	General Purpose Register File .............................................................................	9
	Stack Pointer ......................................................................................................	10
	Instruction Execution Timing...............................................................................	11
	Reset and Interrupt Handling ..............................................................................	11
	AVR ATmega8535 Memories .............................................................	14
	In-System Reprogrammable Flash Program Memory ........................................	14
	SRAM Data Memory...........................................................................................	15
	EEPROM Data Memory......................................................................................	16
	I/O Memory .........................................................................................................	21
	System Clock and Clock Options .....................................................	22
	Clock Systems and their Distribution ..................................................................	22
	Clock Sources.....................................................................................................	23
	Default Clock Source ..........................................................................................	23
	Crystal Oscillator.................................................................................................	23
	Low-frequency Crystal Oscillator ........................................................................	26
	External RC Oscillator ........................................................................................	26
	Calibrated Internal RC Oscillator ........................................................................	27
	External Clock.....................................................................................................	29
	Timer/Counter Oscillator .....................................................................................	29
	Power Management and Sleep Modes..............................................	30
	Idle Mode ............................................................................................................	31
	ADC Noise Reduction Mode ...............................................................................	31
	Power-down Mode..............................................................................................	31
	Power-save Mode ...............................................................................................	31
	Standby Mode.....................................................................................................	32
	Extended Standby Mode ....................................................................................	32
		i
2502B–AVR–09/02

Minimizing Power Consumption .........................................................................	33
System Control and Reset .................................................................	34
Internal Voltage Reference .................................................................................	39
Watchdog Timer .................................................................................................	39
Timed Sequences for Changing the Configuration of the Watchdog Timer .......	43
Interrupts .............................................................................................	44
Interrupt Vectors in ATmega8535 .......................................................................	44
I/O-Ports...............................................................................................	49
Introduction .........................................................................................................	49
Ports as General Digital I/O ................................................................................	50
Alternate Port Functions .....................................................................................	54
Register Description for I/O-Ports .......................................................................	63
External Interrupts..............................................................................	65
8-bit Timer/Counter0 with PWM.........................................................	68
Overview .............................................................................................................	68
Timer/Counter Clock Sources.............................................................................	69
Counter Unit........................................................................................................	69
Output Compare Unit..........................................................................................	70
Compare Match Output Unit ...............................................................................	72
Modes of Operation ............................................................................................	73
Timer/Counter Timing Diagrams.........................................................................	77
8-bit Timer/Counter Register Description ...........................................................	79
Timer/Counter0 and Timer/Counter1 Prescalers .............................	83
16-bit Timer/Counter1.........................................................................	85
Overview .............................................................................................................	85
Accessing 16-bit Registers .................................................................................	88
Timer/Counter Clock Sources.............................................................................	91
Counter Unit........................................................................................................	91
Input Capture Unit...............................................................................................	92
Output Compare Units ........................................................................................	94
Compare Match Output Unit ...............................................................................	96
Modes of Operation ............................................................................................	97
Timer/Counter Timing Diagrams.......................................................................	105
16-bit Timer/Counter Register Description .......................................................	107
8-bit Timer/Counter2 with PWM and Asynchronous Operation ...	114
Overview ...........................................................................................................	114
Timer/Counter Clock Sources...........................................................................	115
Counter Unit......................................................................................................	116

ii ATmega8535(L)

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ATmega8535(L)

Output Compare Unit........................................................................................	116
Compare Match Output Unit .............................................................................	118
Modes of Operation ..........................................................................................	119
Timer/Counter Timing Diagrams.......................................................................	123
8-bit Timer/Counter Register Description .........................................................	125
Asynchronous Operation of the Timer/Counter ................................................	128
Timer/Counter Prescaler...................................................................................	131
Serial Peripheral Interface – SPI......................................................	133
SS Pin Functionality..........................................................................................	137
Data Modes ......................................................................................................	140
USART ...............................................................................................	141
Overview ...........................................................................................................	141
Clock Generation ..............................................................................................	142
Frame Formats .................................................................................................	145
USART Initialization..........................................................................................	146
Data Transmission – The USART Transmitter .................................................	148
Data Reception – The USART Receiver ..........................................................	151
Asynchronous Data Reception .........................................................................	154
Multi-processor Communication Mode .............................................................	158
Accessing UBRRH/UCSRC Registers..............................................................	159
USART Register Description ............................................................................	160
Examples of Baud Rate Setting ........................................................................	166
Two-wire Serial Interface .................................................................	170
Features............................................................................................................	170
Two-wire Serial Interface Bus Definition...........................................................	170
Data Transfer and Frame Format .....................................................................	171
Multi-master Bus Systems, Arbitration and Synchronization ............................	173
Overview of the TWI Module ............................................................................	175
TWI Register Description ..................................................................................	177
Using the TWI ...................................................................................................	181
Transmission Modes.........................................................................................	184
Multi-master Systems and Arbitration ...............................................................	197
Analog Comparator ..........................................................................	199
Analog Comparator Multiplexed Input ..............................................................	201
Analog-to-Digital Converter.............................................................	202
Features............................................................................................................	202
Operation ..........................................................................................................	203
Starting a Conversion .......................................................................................	204
Prescaling and Conversion Timing ...................................................................	205
Changing Channel or Reference Selection ......................................................	208
ADC Noise Canceler.........................................................................................	210
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2502B–AVR–09/02

ADC Conversion Result....................................................................................	214
Boot Loader Support – Read-While-Write Self-Programming......	220
Boot Loader Features .......................................................................................	220
Application and Boot Loader Flash Sections ....................................................	220
Read-While-Write and No Read-While-Write Flash Sections ...........................	220
Boot Loader Lock Bits.......................................................................................	222
Entering the Boot Loader Program ...................................................................	223
Addressing the Flash during Self-Programming ...............................................	225
Self-Programming the Flash .............................................................................	226
Memory Programming......................................................................	233
Program And Data Memory Lock Bits ..............................................................	233
Fuse Bits...........................................................................................................	234
Signature Bytes ................................................................................................	235
Calibration Byte ................................................................................................	235
Parallel Programming Parameters, Pin Mapping, and Commands ..................	236
Parallel Programming .......................................................................................	238
Serial Downloading ...........................................................................................	247
Electrical Characteristics.................................................................	252
External Clock Drive Waveforms ......................................................................	254
External Clock Drive .........................................................................................	254
Two-wire Serial Interface Characteristics .........................................................	255
SPI Timing Characteristics ...............................................................................	257
ADC Characteristics – Preliminary Data...........................................................	259
ATmega8535 Typical Characteristics – Preliminary Data.............	260
Register Summary ............................................................................	261
Instruction Set Summary .................................................................	263
Ordering Information(1) .....................................................................	266
Packaging Information .....................................................................	267
44A ...................................................................................................................	267
40P6 .................................................................................................................	268
44J ....................................................................................................................	269
44M1-A .............................................................................................................	270
Data Sheet Change Log for ATmega8535 ......................................	271
Changes from Rev. 2502A-06/02 to Rev. 2502B-09/02 ...................................	271
Table of Contents ..................................................................................	i

iv ATmega8535(L)

2502B–AVR–09/02

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