Scripts

About Scripts

A script is a small section of code that Great Cow BASIC runs when it starts to compile a program. Uses include performing calculations that are required to adjust the program for different chip frequencies.

Scripts are not compiled or downloaded to the microcontroller - Great Cow BASIC reads them, executes them, then removes them from the program and then the results calculated can be used as constants in the user program.

Inside a script, constants are treated like variables. Scripts can read the values of constants, and set them to contain new values.

Using Scripts

Scripts start with #script and end with #endscript. Inside, they can consist of the following commands:

    If
    Assignment (=)
    Error
    Warning
    Int()

If is similar to the If command in normal Great Cow BASIC code, except that it does not have an Else clause. It is used to compare the values of the script constants.

The = sign is identical to that in Great Cow BASIC programs. The constant that is to be set goes on the left side of the = and the new value goes to the right of the =.

Error is used to display an error message. Anything after the Error command is displayed at the end of compilation, and is saved in the error log for the program.

Warning is used to display a warning message. Anything after the Warning command is displayed at the end of compilation but warning does not halt compilation.

Int() will calculate the integer value of a calculation. Using Int() is critical to set the constant to the integer component of the calculation.

Notes:

Use Warning to display constant values when creating and debugging scripts.

Scripts have a limited syntax and limited error checking when compiling. The compiler may halt if you get something wrong.

Scripts that are incorrectly formatted may also halt the compiler or return unrelated error.

Scripts used for calculations should use the Int( expression ) where you may have a floating point numbers returned.
Scripts do use floating point for all calculations and a failure to use Int() may set the script constant and the resulting constant to 0.

Scripts may require that complex math expressions may require definition in multiple steps/line to simplify the calculation.
The returned value could be incorrect if simplification is not implemented.

Scripts can only access existing constants both user and system defined.

User defines variables are not accessible within the scope of a script.

Scripts has precendence over #define. A #define constant statements are read first, then scripts run. So, a script will always overwrite a constant that was set with #define.

Use Warning to display constants values when creating and debugging scripts.

Example Script

This script is used in the pwm.h file. It takes the values of the user defined constants PWM_Freq, PWM_Duty and system constant ChipMHz and calculates the results using the equations. These calculation are based on information from a Microchip PIC datasheet to calculate the correct values to setup Pulse Width Modulation (PWM).

    #script
        PR2Temp = INT((1/PWM_Freq)/(4*(1/(ChipMHz*1000))))
        T2PR = 1
        If PR2Temp > 255 Then
            PR2Temp = INT((1 / PWM_Freq) / (16 * (1 / (ChipMHz * 1000))))
            T2PR = 4
            If PR2Temp > 255 Then
                PR2Temp = INT(( 1 / PWM_Freq) / (64 * (1 / (ChipMHz * 1000))))
                T2PR = 16
                If PR2Temp > 255 Then
                    Error Invalid PWM Frequency value
                End If
            End If
        End If

        DutyCycle = (PWM_Duty * 10.24) * PR2Temp / 1024
        DutyCycleH = (DutyCycle AND 1020) / 4
        DutyCycleL = DutyCycle AND 3
    #endscript

During the execution of the script the calculations and assignment uses the constants in the script.

After this script has completed the constants PR2Temp, DutyCycleH and DutyCycleL are set using the constants and/or the calculations.

The constants assigned in this script, PR2Temp, DutyCycleH and DutyCycleL, are made available as constants in the user program.