The third and last timer module of the PIC 16F88 is the Timer2 module. This module is originated to work along with the PWM module of the PIC. It can be used of course as a timer as well. It is an 8-bit counter, and has a programmable prescaler and postscaler. It has only one input source, the internal instruction clock (device oscillator/4). Timer2 module is equipped also with a Period Register.

The Timer2 value register is located in the first BANK (BANK0) and is named TMR2. This module will be turned off after Sleep operation. To set up and control the Timer1 module, you need to access the T2CON register located also in BANK0. The bits of this register are explained bellow:

These 4 bits are the "Timer2 Output Postscale Select bits". They control the postscaler division rate:

• 0000: 1:1 division
• 0001: 1:2 division
• 0010: 1:3 division
• 0011: 1:4 division
• 0100: 1:5 division
• 0101: 1:6 division
• 0110: 1:7 division
• 0111: 1:8 division
• 1000: 1:9 division
• 1001: 1:10 division
• 1010: 1:11 division
• 1011: 1:12 division
• 1100: 1:13 division
• 1101: 1:14 division
• 1110: 1:15 division
• 1111: 1:16 division

This bit is named "Timer2 On bit". The Timer2 module can be turned on and off through this bit:

• 0: Timer2 is off
• 1: Timer2 is on

These 2 bits are the "Timer2 Clock Prescale Select bits". They control the prescaler division rate:

• 00: 1:1 division
• 01: 1:4 division
• 1x: 1:16 division

The Timer2 module is equipped with a period register. This register is named "PR2" and is located in BANK1. The TMR2 register is increased, until it is matched to the PR2 register. When this happens, on the next increament cycle, the TMR2 register will be cleared and the count will restart from 0x00. The PR2 register is both readable and writable. It is located BEFORE the postscaler, which you must take into account when setting the value. The postscaler division is NOT taken into account when comparing the PR2 to the TMR2 register!

The Timer2 module has an 8-bit register for the counts, the TMR2 register. This means that it can count up to 255. If the TMR2 value is 255 (0xFF) and it is increased once more, it will become 0 (0x00) and the TMR2 interrupt shall be raised. The Timer2 interrupt can be controlled by the PIE1 register bit 1 (TMR2IE: TMR2 Overflow Interrupt Enable bit). When the Timer2 Interrupt is raised, the PIR1 bit 1 (TMR2IF: TMR2 Overflow Interrupt Flag bit) is raised to indicate that the TMR2 interrupt is occurred. The TMR2IF must be cleared in software (BCF PIR1,TMR2IF) for the TMR2 interrupt to be re-enabled. More info about the PIC Interrupts can be found in this link.

For the sake of understanding, find below some examples on how to setup the Timer2 module.

          MOVLW b'01111011'     ;
          MOVWF T2CON           ; Prescaler = 1:16 | Postscaler = 1:16 | Stop Timer2
          BANK1                 ; Go to BANK 1
          MOVLW 0xFF            ;
          MOVWF PR2             ; Set PR2 register to 0xFF
          BANK0                 ; Go to BANK 0
          BSF T2CON,TMR2ON      ; Start Timer2

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Basics       What will you need       Choosing the right PICThe MPLAB       Getting familiar with the MPLAB environment       Creating a new project       Open and close projects       Creating new files and including them in the project       Your very first assembly program       Compile a program and transfer to the PICSection 1: Beginner's theoryMemory Organization       The Data Memory Organization       The Program Memory OrganizationThe instructions       General knowledge about instructions       Value Loading Instructions       Program Flow Instructions       Mathematic Instructions       Logic Function Instructions       Bit Orientated Instructions       Byte Orientated Instructions       Miscellaneous InstructionsThe Basic Special Function Registers       The Status Register       The Option_Reg Register       The TRIS and PORT registersBeginner's PIC Tutorials       How to use our PIC Tutorials       A Pushbutton turning an LED on and off       A Simple LED Flasher       Interfacing Multiple Switches - The internal Pull-Up resistors       An LED Sequencer       Interface a Single 7seg Digit       Interface Multiple 7seg Digits       A 3-digits Decimal Counter       A Clever ButtonSection 2: Intermediate theory       Instruction Cycle Duration and Calculated Delays       The Timer Modules - Timer0       The Timer Modules - Timer1       The Timer Modules-Timer2

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