TIMERS IN LPC 2148

Features

Applications

• Interval Timer for Counting internal events• Free running timer• Pulse Width Modulator

Pins for Timers

Timer Register

• TC gets incremented by 1 for every PR+1 cycles• PR register specifies the maximum value of PC• PC will be incremented for every single clock cycle until it reaches PR

then it will be RESET• Example• Before 1st clock pulse• TC = 0 ;• PR = 0 ; (has to be initialized by User)• PC = 0 ; (Read Only)• After 1st clock pulse• TC = 1 ;• PR = 0 ; (has to be initialized by User)• PC = 1 ; (Read Only) then again becomes PC = 0;

MATCH TYPES

• Internal Match (Action is performed Internally)• External Match (Action is performed Externally i.e., on Pins)• Match channels and its Registers• CH0 – MR0 register• CH1 – MR1 register• CH2 – MR2 register• CH3 – MR3 register

Match Registers (MR0 – MR3)

• The Match register values are continuously compared to the Timer Counter value. When the two values are equal, actions can be triggered automatically. The action possibilities are to generate an interrupt, reset the Timer Counter or stop the timer. Actions are controlled by the settings in the MCR register• Always TC is compared with MR0-MR3 registers• If any match is generated then a particular action can be performed• Action can be selected by using MCR Register.

Capture Channels and its Registers

• CH0 – CR0 Register• CH1 – CR1 Register• CH2 – CR2 Register• CH3 – CR3 Register• For any external events on Capture Pins TC register is stored in

respective Capture Channel Register

Capture Control

External Match

• External Match Pins• MAT0.0 (2pins): P0.3 and P0.22• MAT0.1 (2pins): P0.5 and P0.27• MAT0.2 (2pins): P0.16 and P0.28• MAT0.3 (1pin): P0.29• MAT1.0 (1pin): P0.12• MAT1.1 (1pin): P0.13• MAT1.2 (2pins): P0.17 and P0.19• MAT1.3 (2pins): P0.18 and P0.20• Whenever TC equals any of match register then an action can be performed on the

above match pins and that action is decided by EMR Register