Datasheet ATtiny28L, ATtiny28V (Atmel) - 7
| Manufacturer | Atmel |
| Pages / Page | 81 / 7 — ATtiny28L/V. System Clock and. Clock Options. Table 1. Clock Option. … |
| File Format / Size | PDF / 680 Kb |
| Document Language | English |
ATtiny28L/V. System Clock and. Clock Options. Table 1. Clock Option. CKSEL3..0. Internal RC Oscillator. Calibrated Internal RC
Model Line for this Datasheet
Text Version of Document
link to page 46
ATtiny28L/V System Clock and
The device has the following clock source options, selectable by Flash Fuse bits as
Clock Options
shown in Table 1.
Table 1.
Device Clocking Option Select
Clock Option CKSEL3..0
External Crystal/Ceramic Resonator 1111 - 1010 External Low-frequency Crystal 1001 - 1000 External RC Oscillator 0111 - 0101 Internal RC Oscillator 0100 - 0010 External Clock 0001 - 0000 Note: “1” means unprogrammed, “0” means programmed. The various choices for each clocking option give different start-up times as shown in Table 5 on page 16.
Internal RC Oscillator
The internal RC oscillator option is an on-chip calibrated oscillator running at a nominal frequency of 1.2 MHz. If selected, the device can operate with no external components. The device is shipped with this option selected.
Calibrated Internal RC
The calibrated internal oscillator provides a fixed 1.2 MHz (nominal) clock at 3V and
Oscillator
25°C. This clock may be used as the system clock. This oscillator can be calibrated by writing the calibration byte to the OSCCAL register. When this oscillator is used as the chip clock, the Watchdog oscillator will still be used for the Watchdog Timer and for the reset time-out. For details on how to use the pre-programmed calibration value, see the section “Calibration Byte” on page 46.
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier, which can be configured for use as an on-chip oscillator, as shown in Figure 5. Either a quartz crystal or a ceramic resonator may be used. When the INTCAP fuse is programmed, internal load capacitors with typical values 50 pF are connected between XTAL1/XTAL2 and ground.
Figure 5.
Oscillator Connections MAX 1 HC BUFFER HC C2 XTAL2 C1 XTAL1 GND Note: 1. When using the MCU oscillator as a clock for an external device, an HC buffer should be connected as indicated in the figure.
External Clock
To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.
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1062F–AVR–07/06 Document Outline Features Pin Configurations Description Block Diagram Pin Descriptions VCC GND Port A (PA3..PA0) Port B (PB7..PB0) Port D (PD7..PD0) XTAL1 XTAL2 RESET Architectural Overview ALU - Arithmetic Logic Unit Subroutine and Interrupt Hardware Stack General-purpose Register File Status Register Status Register - SREG System Clock and Clock Options Internal RC Oscillator Calibrated Internal RC Oscillator Crystal Oscillator External Clock External RC Oscillator Register Description Oscillator Calibration Register - OSCCAL Memories I/O Memory Program and Data Addressing Modes Register Direct, Single Register Rd Register Indirect Register Direct, Two Registers Rd and Rr I/O Direct Relative Program Addressing, RJMP and RCALL Constant Addressing Using the LPM Instruction Memory Access and Instruction Execution Timing Flash Program Memory Sleep Modes Idle Mode Power-down Mode System Control and Reset Reset Sources Power-on Reset External Reset Watchdog Reset Register Description MCU Control and Status Register - MCUCS Interrupts Reset and Interrupt Interrupt Handling Interrupt Response Time External Interrupt Low-level Input Interrupt Register Description Interrupt Control Register - ICR Interrupt Flag Register - IFR I/O Ports Port A Port A as General Digital I/O Alternate Function of PA2 Port A Schematics Port B Port B as General Digital Input Alternate Functions of Port B Port B Schematics Port D Port D as General Digital I/O Register Description Port A Data Register - PORTA Port A Control Register - PACR Port A Input Pins Address - PINA Port B Input Pins Address - PINB Port D Data Register - PORTD Port D Data Direction Register - DDRD Port D Input Pins Address - PIND Timer/Counter0 Timer/Counter Prescaler Register Description Timer/Counter0 Control Register - TCCR0 Timer Counter 0 - TCNT0 Watchdog Timer Register Description Watchdog Timer Control Register - WDTCR Hardware Modulator Register Description Modulation Control Register - MODCR Analog Comparator Register Description Analog Comparator Control and Status Register - ACSR Memory Programming Program Memory Lock Bits Fuse Bits Signature Bytes Calibration Byte Programming the Flash Parallel Programming Signal Names Enter Programming Mode Chip Erase Programming the Flash Reading the Flash Programming the Fuse Bits Programming the Lock Bits Reading the Fuse and Lock Bits Reading the Signature Bytes and Calibration Byte Parallel Programming Characteristics Electrical Characteristics Absolute Maximum Ratings DC Characteristics External Clock Drive Waveforms External Clock Drive Typical Characteristics Register Summary Instruction Set Summary Ordering Information Packaging Information 32A 28P3 32M1-A Errata All revisions Datasheet Revision History Rev - 01/06G Rev - 01/06G Rev - 03/05F Table of Contents
ATtiny28L/V System Clock and
The device has the following clock source options, selectable by Flash Fuse bits as
Clock Options
shown in Table 1.
Table 1.
Device Clocking Option Select
Clock Option CKSEL3..0
External Crystal/Ceramic Resonator 1111 - 1010 External Low-frequency Crystal 1001 - 1000 External RC Oscillator 0111 - 0101 Internal RC Oscillator 0100 - 0010 External Clock 0001 - 0000 Note: “1” means unprogrammed, “0” means programmed. The various choices for each clocking option give different start-up times as shown in Table 5 on page 16.
Internal RC Oscillator
The internal RC oscillator option is an on-chip calibrated oscillator running at a nominal frequency of 1.2 MHz. If selected, the device can operate with no external components. The device is shipped with this option selected.
Calibrated Internal RC
The calibrated internal oscillator provides a fixed 1.2 MHz (nominal) clock at 3V and
Oscillator
25°C. This clock may be used as the system clock. This oscillator can be calibrated by writing the calibration byte to the OSCCAL register. When this oscillator is used as the chip clock, the Watchdog oscillator will still be used for the Watchdog Timer and for the reset time-out. For details on how to use the pre-programmed calibration value, see the section “Calibration Byte” on page 46.
Crystal Oscillator
XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier, which can be configured for use as an on-chip oscillator, as shown in Figure 5. Either a quartz crystal or a ceramic resonator may be used. When the INTCAP fuse is programmed, internal load capacitors with typical values 50 pF are connected between XTAL1/XTAL2 and ground.
Figure 5.
Oscillator Connections MAX 1 HC BUFFER HC C2 XTAL2 C1 XTAL1 GND Note: 1. When using the MCU oscillator as a clock for an external device, an HC buffer should be connected as indicated in the figure.
External Clock
To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.
7
1062F–AVR–07/06 Document Outline Features Pin Configurations Description Block Diagram Pin Descriptions VCC GND Port A (PA3..PA0) Port B (PB7..PB0) Port D (PD7..PD0) XTAL1 XTAL2 RESET Architectural Overview ALU - Arithmetic Logic Unit Subroutine and Interrupt Hardware Stack General-purpose Register File Status Register Status Register - SREG System Clock and Clock Options Internal RC Oscillator Calibrated Internal RC Oscillator Crystal Oscillator External Clock External RC Oscillator Register Description Oscillator Calibration Register - OSCCAL Memories I/O Memory Program and Data Addressing Modes Register Direct, Single Register Rd Register Indirect Register Direct, Two Registers Rd and Rr I/O Direct Relative Program Addressing, RJMP and RCALL Constant Addressing Using the LPM Instruction Memory Access and Instruction Execution Timing Flash Program Memory Sleep Modes Idle Mode Power-down Mode System Control and Reset Reset Sources Power-on Reset External Reset Watchdog Reset Register Description MCU Control and Status Register - MCUCS Interrupts Reset and Interrupt Interrupt Handling Interrupt Response Time External Interrupt Low-level Input Interrupt Register Description Interrupt Control Register - ICR Interrupt Flag Register - IFR I/O Ports Port A Port A as General Digital I/O Alternate Function of PA2 Port A Schematics Port B Port B as General Digital Input Alternate Functions of Port B Port B Schematics Port D Port D as General Digital I/O Register Description Port A Data Register - PORTA Port A Control Register - PACR Port A Input Pins Address - PINA Port B Input Pins Address - PINB Port D Data Register - PORTD Port D Data Direction Register - DDRD Port D Input Pins Address - PIND Timer/Counter0 Timer/Counter Prescaler Register Description Timer/Counter0 Control Register - TCCR0 Timer Counter 0 - TCNT0 Watchdog Timer Register Description Watchdog Timer Control Register - WDTCR Hardware Modulator Register Description Modulation Control Register - MODCR Analog Comparator Register Description Analog Comparator Control and Status Register - ACSR Memory Programming Program Memory Lock Bits Fuse Bits Signature Bytes Calibration Byte Programming the Flash Parallel Programming Signal Names Enter Programming Mode Chip Erase Programming the Flash Reading the Flash Programming the Fuse Bits Programming the Lock Bits Reading the Fuse and Lock Bits Reading the Signature Bytes and Calibration Byte Parallel Programming Characteristics Electrical Characteristics Absolute Maximum Ratings DC Characteristics External Clock Drive Waveforms External Clock Drive Typical Characteristics Register Summary Instruction Set Summary Ordering Information Packaging Information 32A 28P3 32M1-A Errata All revisions Datasheet Revision History Rev - 01/06G Rev - 01/06G Rev - 03/05F Table of Contents
