- •Features
- •Pin Configurations
- •Overview
- •Block Diagram
- •Disclaimer
- •Pin Descriptions
- •Port A (PA7..PA0)
- •Port B (PB7..PB0)
- •Port C (PC7..PC0)
- •Port D (PD7..PD0)
- •Port E(PE2..PE0)
- •RESET
- •XTAL1
- •XTAL2
- •AVR CPU Core
- •Introduction
- •Architectural Overview
- •Status Register
- •Stack Pointer
- •Interrupt Response Time
- •In-System Reprogrammable Flash Program memory
- •SRAM Data Memory
- •Data Memory Access Times
- •EEPROM Data Memory
- •EEPROM Read/Write Access
- •I/O Memory
- •Overview
- •Address Latch Requirements
- •Pull-up and Bus Keeper
- •Timing
- •Using all Locations of External Memory Smaller than 64 KB
- •Using all 64KB Locations of External Memory
- •Clock Systems and their Distribution
- •Clock Sources
- •Default Clock Source
- •Crystal Oscillator
- •External RC Oscillator
- •External Clock
- •Idle Mode
- •Power-down Mode
- •Standby Mode
- •Analog Comparator
- •Brown-out Detector
- •Internal Voltage Reference
- •Watchdog Timer
- •Port Pins
- •Resetting the AVR
- •Reset Sources
- •Power-on Reset
- •External Reset
- •Brown-out Detection
- •Watchdog Reset
- •Watchdog Timer
- •Timed Sequences for Changing the Configuration of the Watchdog Timer
- •Safety Level 0
- •Safety Level 1
- •Safety Level 2
- •Interrupts
- •Moving Interrupts between Application and Boot Space
- •I/O Ports
- •Introduction
- •Configuring the Pin
- •Reading the Pin Value
- •Unconnected pins
- •Alternate Port Functions
- •Alternate Functions of Port A
- •Alternate Functions Of Port B
- •Alternate Functions of Port C
- •Alternate Functions of Port D
- •Alternate Functions of Port E
- •Register Description for I/O Ports
- •External Interrupts
- •8-bit Timer/Counter0 with PWM
- •Overview
- •Registers
- •Definitions
- •Counter Unit
- •Output Compare Unit
- •Force Output Compare
- •Modes of Operation
- •Normal Mode
- •Fast PWM Mode
- •Phase Correct PWM Mode
- •Internal Clock Source
- •Prescaler Reset
- •External Clock Source
- •16-bit Timer/Counter1
- •Overview
- •Registers
- •Definitions
- •Compatibility
- •Counter Unit
- •Input Capture Unit
- •Input Capture Trigger Source
- •Noise Canceler
- •Using the Input Capture Unit
- •Output Compare Units
- •Force Output Compare
- •Modes of Operation
- •Normal Mode
- •Fast PWM Mode
- •Phase Correct PWM Mode
- •Slave Mode
- •Master Mode
- •Data Modes
- •USART
- •Single USART
- •Clock Generation
- •External Clock
- •Synchronous Clock Operation
- •Frame Formats
- •Parity Bit Calculation
- •USART Initialization
- •Sending Frames with 5 to 8 Data Bits
- •Sending Frames with 9 Data Bits
- •Parity Generator
- •Disabling the Transmitter
- •Receiving Frames with 5 to 8 Data Bits
- •Receiving Frames with 9 Data Bits
- •Receiver Error Flags
- •Parity Checker
- •Disabling the Receiver
- •Flushing the Receive Buffer
- •Asynchronous Data Recovery
- •Using MPCM
- •Write Access
- •Read Access
- •Analog Comparator
- •Features
- •Application Section
- •Boot Loader Lock bits
- •Performing a Page Write
- •Using the SPM Interrupt
- •Setting the Boot Loader Lock bits by SPM
- •Reading the Fuse and Lock bits from Software
- •Preventing Flash Corruption
- •Simple Assembly Code Example for a Boot Loader
- •Program and Data Memory Lock bits
- •Fuse bits
- •Latching of Fuses
- •Signature Bytes
- •Calibration Byte
- •Calibration Byte
- •Signal Names
- •Parallel Programming
- •Enter Programming Mode
- •Chip Erase
- •Programming the Flash
- •Programming the EEPROM
- •Reading the Flash
- •Reading the EEPROM
- •Programming the Lock bits
- •Reading the Signature Bytes
- •Reading the Calibration Byte
- •Serial Downloading
- •Data Polling Flash
- •Data Polling EEPROM
- •Electrical Characteristics
- •Absolute Maximum Ratings*
- •External Clock Drive Waveforms
- •External Clock Drive
- •External Data Memory Timing
- •Active Supply Current
- •Idle Supply Current
- •Standby Supply Current
- •Pin Pull-up
- •Pin Driver Strength
- •Internal Oscillator Speed
- •Register Summary
- •Instruction Set Summary
- •Ordering Information
- •Packaging Information
- •Errata
- •ATmega8515(L) Rev. B
- •Changes from Rev. 2512F-12/03 to Rev. 2512G-03/05
- •Changes from Rev. 2512F-12/03 to Rev. 2512E-09/03
- •Changes from Rev. 2512D-02/03 to Rev. 2512E-09/03
- •Changes from Rev. 2512C-10/02 to Rev. 2512D-02/03
- •Changes from Rev. 2512B-09/02 to Rev. 2512C-10/02
- •Changes from Rev. 2512A-04/02 to Rev. 2512B-09/02
- •Table of Contents
Timer/Counter Clock
Sources
Counter Unit
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is selected by the Clock Select logic which is controlled by the Clock Select (CS12:0) bits located in the Timer/Counter Control Register B (TCCR1B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 94.
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit. Figure 48 shows a block diagram of the counter and its surroundings.
Figure 48. Counter Unit Block Diagram
DATA BUS (8-bit)
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TOVn |
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(Int.Req.) |
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TEMP (8-bit) |
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TCNTnH (8-bit) |
TCNTnL (8-bit) |
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Control Logic |
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clkTn |
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Clear |
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TCNTn (16-bit Counter) |
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Signal description (internal signals):
Count |
Increment or decrement TCNT1 by 1. |
Direction |
Select between increment and decrement. |
Clear |
Clear TCNT1 (set all bits to zero). |
clkT1 |
Timer/Counter clock. |
TOP |
Signalize that TCNT1 has reached maximum value. |
BOTTOM |
Signalize that TCNT1 has reached minimum value (zero). |
The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNT1H) containing the upper eight bits of the counter, and Counter Low (TCNT1L) containing the lower eight bits. The TCNT1H Register can only be indirectly accessed by the CPU. When the CPU does an access to the TCNT1H I/O location, the CPU accesses the high byte temporary register (TEMP). The temporary register is updated with the TCNT1H value when the TCNT1L is read, and TCNT1H is updated with the temporary register value when TCNT1L is written. This allows the CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus. It is important to notice that there are special cases of writing to the TCNT1 Register when the counter is counting that will give unpredictable results. The special cases are described in the sections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented at each Timer Clock (clkT1). The clkT1 can be generated from an external or internal clock source, selected by the Clock Select bits (CS12:0). When no clock source is selected (CS12:0 = 0) the timer is stopped. However, the TCNT1 value can be accessed by the CPU, independent of whether clkT1 is present or not. A CPU write overrides (has priority over) all counter clear or count operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits (WGM13:0) located in the Timer/Counter Control Registers A and B (TCCR1A and TCCR1B). There are close connections between how the counter behaves (counts) and
102 ATmega8515(L)
2512G–AVR–03/05