• How to use the HLVD module as a low voltage monitor

    In hopes this might help someone avoid the time it took me to learn this I will make this contribution of code as a solution to using the HLVD module as a low Vdd voltage monitor. I was able to resolve this with some offline support from Darrel Taylor. This process has been tested and it works!

    First, you need to setup a DT_INTS-18 interrupt for the HLVD module. You can find DT_INTS-18 version 3.4 here: http://www.picbasic.co.uk/forum/show...2826#post82826

    INT_LIST  macro    ; IntSource,         Label,  Type, ResetFlag?
            ;INT_Handler   USB_Handler
            INT_Handler   HLVD_INT,        _LowVolt, PBP,  yes
        INT_CREATE                ; Creates the interrupt processor
    Here are the voltage settings for the PIC18F4550. Check the data sheet for your device.

    Then you need to insert this code in your main program loop to setup the use of the HLVD module.

     ' Set registers for using HLVD feature per section 24.2 of the 18F4550 data sheet
              ' Step 1-Disable the module by clearing HLVDCON.4
                    HLVDCON.4 = 0     ' Implement Step 1           
              ' Step2 HLVD3:HLVDL0=1101 'Set the trip point at Vdd=4.33 vdc
              ' Step3 HLVDCON.7=0 'Set VDIRMAG=0 to detect low voltage transition
              ' Step4 HLVDCON.4=1 'Enable the HLVD module
                      HLVDCON = %00011101   'Implements Steps 2-4
              ' Clear the HLVDIF interrupt flag (PIR2<2>)
                     PIR2.2 = 0
    Then you need to create an interrupt service routine (ISR) near the end of your code as follows:

       ' Blink LED_RED 5X to indicate Low Battery voltage detected
            For i = 0 to 4
               HIGH LED_RED
               Pause 500
               LOW LED_RED
               PAUSE 500
    @ INT_DISABLE HLVD_INT      ; This statement very important, else code will lockup on exit
                                                ; from the ISR to main program. 
            ' Resume Main Program
    '------------------{ End of Interrupt Handlers }-------------------------
    Then you need to insert this assembler statement in your code wherever you want to test for a low Vdd voltage condition. I insert this in my main loop so that regardless of what other events are occuring, whenever the above ISR completes, the mainloop sets up the HLVD module for another low voltage interrupt.

    @    INT_ENABLE   HLVD_INT               ; enable HLVD interrupt
    I hope this might help someone!
    This article was originally published in forum thread: How to use the HLVD module as a low voltage monitor started by jellis00 View original post