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watchdog not working in 87c520

Baruch A

A strange situation where an internal watchdog reset implementation seems not to work on the 87c520 target while it does work ok when using the Ceibo ICE.

Seems like the reset occurs but unclear where the PC jumps to because the SW does not restart properly but rather stays "stuck" (we know it enters the if (status) passage). With the ICE the program does start ok.

What we do is enable the watchdog timer in the program. In the interrupt handler (ISR 12) depending on some status, we enable the reset itself. All this occurs, but then for the target the program does not go into running normally.

Any ideas?
Thanks,
Baruch



if ( status ) //
{
TA = 0xAA ; //Accessing timed access in order to start the watchdog timer
TA = 0x55 ; //
EWT = 1 ; // Enable WatchDog timer reset

TA = 0xAA; //Accessing timed access in order to start the watchdog timer
TA = 0x55; //
WDIF = 0 ; // watch dog flag clear
}

else
{
TA = 0xAA; //Accessing timed access in order to start the watchdog timer
TA = 0x55; //
WDIF = 0 ; // watch dog flag clear

TA = 0xAA ; //Accessing timed access in order to start the watchdog timer
TA = 0x55 ; //
RWT = 1 ; // Restart Watchdog timer

}

Parents
  • 0 in reply to Baruch A

    Hi,
    yes, any reset (either watchdog or external RES pin) set SFRs to their default values except POR flag(s).
    Why do you just not control this flag at first program steps? For example: at first codes just check POR value:
    - if POR=1 then it is first power-on: you do configure flash, make POR=0 by software and wait till watchdog resets MCU;
    - if it is =0 then you make on-chip ROM size equ 0 kb and next instructuon will be fetched from external flash. It is simple.

    Good days!

Reply
  • 0 in reply to Baruch A

    Hi,
    yes, any reset (either watchdog or external RES pin) set SFRs to their default values except POR flag(s).
    Why do you just not control this flag at first program steps? For example: at first codes just check POR value:
    - if POR=1 then it is first power-on: you do configure flash, make POR=0 by software and wait till watchdog resets MCU;
    - if it is =0 then you make on-chip ROM size equ 0 kb and next instructuon will be fetched from external flash. It is simple.

    Good days!

Children
  • 0 in reply to Oleg Sergeev

    Of course. The normal resolution would be to handle the POR and/or the WTRF (WDCON.2) for the watchdog reset flag at the beginning of the EPROM code.
    For various practical reasons we would have liked to avoid modifying the EPROM code, but it seems that we will have to take this course.

    Thanks again,
    Baruch