Datasheet AT90S4434, AT90LS4434, AT90S8535, AT90LS8535 - Preliminary (Atmel) - 6

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Architectural Overview
The fast-access register file concept contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This means that during one single clock cycle, one Arithmetic Logic Unit (ALU) operation is executed. Two operands are output from the register file, the operation is executed, and the result is stored back in the register file - in one clock cycle. Six of the 32 registers can be used as three 16-bits indirect address register pointers for Data Space addressing - enabling efficient address calculations. One of the three address pointers is also used as the address pointer for the constant table look up function. These added function registers are the 16-bits X-register, Y-register and Z-register.
Figure 4.
The AT90S4434/8535 AVR RISC Architecture AVR AT90S4434/8535 Architecture Data Bus 8-bit Program Status Interrupt 2K/4K X 16 Counter and Control Unit Program Memory SPI 32 x 8 Unit Instruction General Register Purpose Registrers Serial UART Instruction Decoder 8-bit Timer/Counter ALU Control Lines 16-bit Timer/Counter with PWM Direct Addressing Indirect Addressing 8-bit Timer/Counter with PWM 256/512 x 8 Data SRAM Watchdog Timer 256/512 x 8 Analog to Digital EEPROM Converter 32 Analog I/O Lines Comparator The ALU supports arithmetic and logic functions between registers or between a constant and a register. Single register operations are also executed in the ALU. Figure 4 shows the AT90S4434/8535 AVR RISC microcontroller architecture. In addition to the register operation, the conventional memory addressing modes can be used on the register file as well. This is enabled by the fact that the register file is assigned the 32 lowermost Data Space addresses ($00 - $1F), allowing them to be accessed as though they were ordinary memory locations.
6 AT90S/LS4434 and AT90S/LS8535
Document Outline Features Description Block Diagram Comparison between AT90S4434 and AT90S8535 Pin Descriptions VCC GND Port A (PA7..PA0) Port B (PB7..PB0) Port C (PC7..PC0) Port D (PD7..PD0) RESET XTAL1 XTAL2 AVCC AREF AGND Clock Options Crystal Oscillator External Clock Timer Oscillator Architectural Overview General Purpose Register File X-register, Y-register And Z-register ALU - Arithmetic Logic Unit In-System Programmable Flash Program Memory SRAM Data Memory Program and Data Addressing Modes Register Direct, Single Register Rd Register Direct, Two Registers Rd And Rr I/O Direct Data Direct Data Indirect With Displacement Data Indirect Data Indirect With Pre-Decrement Data Indirect With Post-Increment Constant Addressing Using the LPM Instruction Indirect Program Addressing, IJMP and ICALL Relative Program Addressing, RJMP and RCALL EEPROM Data Memory Memory Access Times and Instruction Execution Timing I/O Memory Status Register - SREG Stack Pointer - SP Reset and Interrupt Handling Reset Sources Power-On Reset External Reset Watchdog Reset MCU Status Register - MCUSR Interrupt Handling General Interrupt Mask Register - GIMSK General Interrupt Flag Register - GIFR Timer/Counter Interrupt Mask Register - TIMSK Timer/Counter Interrupt Flag Register - TIFR External Interrupts Interrupt Response Time MCU Control Register - MCUCR Sleep Modes Idle Mode Power Down Mode Power Save Mode Timer / Counters Timer/Counter Prescalers 8-bit Timer/Counter0 Timer/Counter0 Control Register - TCCR0 Timer Counter 0 - TCNT0 16-bit Timer/Counter1 Timer/Counter1 Control Register A - TCCR1A Timer/Counter1 Control Register B - TCCR1B Timer/Counter1 - TCNT1H AND TCNT1L Timer/Counter1 Output Compare Register - OCR1AH AND OCR1AL Timer/Counter1 Output Compare Register - OCR1BH AND OCR1BL Timer/Counter1 Input Capture Register - ICR1H AND ICR1L Timer/Counter1 In PWM Mode 8-bit Timer/Counter 2 Timer/Counter2 Control Register - TCCR2 Timer/Counter2 - TCNT2 Timer/Counter2 Output Compare Register - OCR2 Timer/Counter 2 in PWM mode Asynchronous Status Register - ASSR Asynchronous Operation of Timer/Counter2 Watchdog Timer Watchdog Timer Control Register - WDTCR EEPROM Read/Write Access EEPROM Address Register - EEARH and EEARL EEPROM Data Register - EEDR EEPROM Control Register - EECR Prevent EEPROM Corruption Serial Peripheral Interface - SPI SS Pin Functionality Data Modes SPI Control Register - SPCR SPI Status Register - SPSR SPI Data Register - SPDR UART Data Transmission Data Reception UART Control UART I/O Data Register - UDR UART Status Register - USR UART Control Register - UCR Baud Rate Generator UART Baud Rate Register - UBRR Analog Comparator Analog Comparator Control And Status Register - ACSR Analog to Digital Converter Operation Prescaling ADC Noise Canceler Function ADC Multiplexer Select Register - ADMUX ADC Control and Status Register - ADCSR ADC Data Register - ADCL AND ADCH Scanning Multiple Channels ADC Noise Canceling Techniques ADC Characteristics I/O-Ports Port A Port A Data Register - PORTA Port A Data Direction Register - DDRA Port A Input Pins Address - PINA Port A as General Digital I/O Port A Schematics Port B Port B Data Register - PORTB Port B Data Direction Register - DDRB Port B Input Pins Address - PINB Port B As General Digital I/O Alternate Functions Of Port B Port B Schematics Port C Port C Data Register - PORTC Port C Data Direction Register - DDRC Port C Input Pins Address - PINC Port C As General Digital I/O Alternate Functions of Port C Port C Schematics Port D Port D Data Register - PORTD Port D Data Direction Register - DDRD Port D Input Pins Address - PIND Port D As General Digital I/O Alternate Functions Of Port D Port D Schematics Memory Programming Program and Data Memory Lock Bits Fuse Bits Signature Bytes Programming the Flash and EEPROM Parallel Programming Signal Names Enter Programming Mode Chip Erase Programming the Flash Reading the Flash Programming the EEPROM Reading the EEPROM Programming the Fuse Bits Programming the Lock Bits Reading the Fuse and Lock Bits Reading the Signature Bytes Parallel Programming Characteristics Serial Downloading Serial Programming Algorithm Data Polling EEPROM Data Polling Flash Serial Programming Characteristics Electrical Characteristics Absolute Maximum Ratings* DC Characteristics External Clock Drive Waveforms Typical Characteristics Register Summary (Continued) Instruction Set Summary (Continued) Ordering Information Pin Configurations