Datasheet

107
8023F–AVR–07/09
ATmega325P/3250P
15. 16-bit Timer/Counter1
15.1 Features
• True 16-bit Design (i.e., Allows 16-bit PWM)
• Two 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
• Four independent interrupt Sources (TOV1, OCF1A, OCF1B, and ICF1)
15.2 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 sec-
tion are written in general form. A lower case “n” replaces the Timer/Counter number, and a
lower case “x” replaces the Output Compare unit. 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 15-1. For the actual
placement of I/O pins, refer to ”Pinout ATmega3250P” on page 2. 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 loca-
tions are listed in the ”Register Description” on page 128.
The PRTIM1 bit in ”PRR – Power Reduction Register” on page 44 must be written to zero to
enable the Timer/Counter1 module.