17. 16-bit Timer/Counter (Timer/Counter 1, 3, 4, and 5)
17.1 Features
• True 16-bit Design (i.e., Allows 16-bit PWM)
• Three independent Output Compare Units
• Double Buffered Output Compare Registers
• One Input Capture Unit
• Input Capture Noise Canceler
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• External Event Counter
• Twenty independent interrupt sources (TOV1, OCF1A, OCF1B, OCF1C, ICF1, TOV3, OCF3A,
OCF3B, OCF3C, ICF3, TOV4, OCF4A, OCF4B, OCF4C, ICF4, TOV5, OCF5A, OCF5B, OCF5C and
ICF5)
17.2 Overview
The 16-bit Timer/Counter unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement.
Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, and a lower case “x” replaces the Output Compare unit
channel. However, when using the register or bit defines in a program, the precise form must be
used, i.e., TCNT1 for accessing Timer/Counter1 counter value and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 17-1. For the actual
placement of I/O pins, see “TQFP-pinout ATmega640/1280/2560” on page 2 and “Pinout
ATmega1281/2561” on page 4. CPU accessible I/O Registers, including I/O bits and I/O pins,
are shown in bold. The device-specific I/O Register and bit locations are listed in the “Register
Description” on page 158.
The Power Reduction Timer/Counter1 bit, PRTIM1, in “PRR0 – Power Reduction Register 0” on
page 56 must be written to zero to enable Timer/Counter1 module.
The Power Reduction Timer/Counter3 bit, PRTIM3, in “PRR1 – Power Reduction Register 1” on
page 57 must be written to zero to enable Timer/Counter3 module.
The Power Reduction Timer/Counter4 bit, PRTIM4, in “PRR1 – Power Reduction Register 1” on
page 57 must be written to zero to enable Timer/Counter4 module.
The Power Reduction Timer/Counter5 bit, PRTIM5, in “PRR1 – Power Reduction Register 1” on
page 57 must be written to zero to enable Timer/Counter5 module.
Timer/Counter4 and Timer/Counter5 only have full functionality in the ATmega640/1280/2560.
Input capture and output compare are not available in the ATmega1281/2561.
136
ATmega640/1280/1281/2560/2561
2549L–AVR–08/07
ATMEL [ ATMEL ]
