smt_timers

SMT Timers

The Signal Measurement Timer (SMT) capability is a 24-bit counter with advanced clocking and gating logic, which can be configured for measuring a variety of digital signal parameters such as pulse width, frequency and duty cycle, and the time difference between edges on two signals.  

Syntax:

    SETSMT1PERIOD ( 4045000 )        ' 1.000s period
                                     ' a perfect internal clock would be 4000000

    SETSMT2PERIOD ( 9322401 )        ' 4.600s period

    InitSMT1(SMT_FOSC,SMTPres_1)
    InitSMT2(SMT_FOSC4,SMTPres_8)

    On Interrupt SMT1Overflow Call yourSMT1InterruptHandler
    On interrupt SMT2Overflow Call yourSMT1InterruptHandler

    StartSMT1
    StartSMT2

Command Availability:

Available on Microchip microcontrollers with the SMT timer module.

This command set supports the use of the SMT as a 24-bit timer only.

Microchip PIC Microcontrollers have either 1 or 2 Signal Measurement Timers (SMT).   A 24-bit timer allows for very long timer periods/high resolution and can be quite useful for certain applications.   SMT timers support multiple clock sources and prescales.   Interrupt on overflow/match is also supported.

SMT timers will "overflow" when the 24-bit timer value "matches" the 24-bit period registers.

The timer period can be precisely adjusted/set by writing a period value to the respective period register for eact timer.

The maximum period is achieved by a period register value of 16,777,215.   16,777,215 is the default value at POR.   The timer period is also affected by the ChipMhz, TimerSource and Timer Prescale.

The library supports "normal" timer operation of SMT1/SMT2.   The library does not support the advanced signal measurement features.

Explanation:

Commands are detailed in the table below:

Command	Description	Example
InitSMT1( Source,Presscaler )	Source can be one of the below: SMT_AT1_perclk   equates to 6 SMT_MFINTOSC       equates to 5 (500KHz) SMT_MFINTOSC_16 equates to 4 (500Khz / 16) SMT_LFINTOSC       equates to 3 (32Khz) SMT_HFINTOSC      equates to 2 SMT_FOSC4             equates to 1 (FOSC/4) SMT_FOSC               equates to 0 Prescaler can be one of the following: SMTPres_1 equates to 1:1 SMTPres_2 equates to 1:2 SMTPres_4 equates to 1:4 SMTPres_8 equates to 1:8	InitSMT1(SMT_FOSC,SMTPres_1)
InitSMT2( Source,Presscaler )	Source can be one of the below: SMT_AT1_perclk   equates to 6 SMT_MFINTOSC       equates to 5 (500KHz) SMT_MFINTOSC_16 equates to 4 (500Khz / 16) SMT_LFINTOSC       equates to 3 (32Khz) SMT_HFINTOSC      equates to 2 SMT_FOSC4             equates to 1 (FOSC/4) SMT_FOSC               equates to 0 Prescaler can be one of the following: SMTPres_1 equates to 1:1 SMTPres_2 equates to 1:2 SMTPres_4 equates to 1:4 SMTPres_8 equates to 1:8	InitSMT2(SMT_FOSC4,SMTPres_8)
ClearSMT1	Clears the timer. No parameter required.	ClearSMT1
ClearSMT	Clears the timer. No parameter required.	ClearSMT2
SetSMT1( TimerValue )	Sets the timer to the specific value. The value can be 1 to 16777215	SETSMT1(4045000)
SetSMT2( TimerValue )	Sets the timer to the specific value. The value can be 1 to 16777215	SETSMT2(4045000)
StopSMT1	Stops the timer. No parameter required.	StopSMT2
StopSMT2	Stops the timer. No parameter required.
StartSMT1	Starts the timer. No parameter required.	StartSMT1
StartSMT2	Starts the timer. No parameter required.	StartSMT2
SetSMT1Period ( PeriodValue )	Sets the timer period to the specific value. The value can be 1 to 16777215	SETSMT1PERIOD(4045000)
SetSMT2Period ( PeriodValue )	Sets the timer period to the specific value. The value can be 1 to 16777215	SETSMT1PERIOD(9322401)

Example 1 (Microchip Only):

This example will ..

    #Chip 16F18855, 32

    #option explicit
    #Include <SMT_Timers.h>
    #config CLKOUTEN_ON


      '' -------------------LATA-----------------
      '' Bit#:  -7---6---5---4---3---2---1---0---
      '' LED:   ---------------|D5 |D4 |D3 |D1 |-
      ''-----------------------------------------
      ''
      #define LEDD2 PORTA.0
      #define LEDD3 PORTA.1
      #define LEDD4 PORTA.2
      #define LEDD5 PORTA.3
      #define Potentiometer   PORTA.4

      Dir     LEDD2 OUT
      Dir     LEDD3 OUT
      Dir     LEDD4 OUT
      Dir     LEDD5 OUT
      DIR     Potentiometer In


     SETSMT1PERIOD ( 4045000 )        ' 1.000s periodwith the parameters of SMT_FOSC and SMTPres_1 within the clock variance of the interclock
                                      ' a perfect internal clock would be 4000000

     SETSMT1PERIOD ( 9322401 )        ' 4.600s period with the parameters of SMT_FOSC4 and SMTPres_8

     InitSMT1(SMT_FOSC,SMTPres_1)
     InitSMT2(SMT_FOSC4,SMTPres_8)


     On Interrupt SMT1Overflow Call BlinkLEDD2
     On interrupt SMT2Overflow Call BlinkLEDD3

     StartSMT1
     StartSMT2


     Do
       '// Waiting for interrupts

     LOOP


    Sub BlinkLEDD2
      LEDD2 = !LEDD2
    End SUB



    Sub BlinkLEDD3
      LEDD3 = !LEDD3
    End SUB

Supported in <SMT_Timers.h>