SH8 LVW problem

[RobG]

I'd like some assistance with the LVD system in the 9S08SH8 please.

I can't reset the LVWF flag once set.

I'm using ICDHCS08 debugger. Stepping through shows that;

          lda     #%01011100     ; set LVWACK

          sta     $1809                ; SPMSC1

does not clear LVWF (when Vdd > Vlvw).

What is the correct procedure for clearing LVWF please?

Thanks
Rob

[RobG]

Perhaps I could add a bit more information.

Both LVD interupt and polling works in detecting LVWF = 1.
But clearing LVWF is the problem.
Mostly, only reset clears LVWF but sometimes even that does not clear it?????????

The following code is what I am using.

*interupt sub
BrownoutISR
        jsr    BrownoutSub      ; will not return while LVWF = 1
        rti


* Brownout subroutine
* will not exit while LVWF = 1
BrownoutSub
       lda    $1809                 ; get SPMSC1
       bpl    exitBSub             ; if LVWF = 0 then exit

* take action here in case of brownout (just disable outputs)
*       .......
*       .......

* clear flag. rem out appropriate option depending on polling or urupt being
used
*     lda     #%01011101     ; set LVWACK (polling method)
       lda     #%01111101     ; set LVWACK (irupt method)
       sta     $1809                 ; write to SPMSC1
       bra    BrownoutSub      ; stay in loop till Vdd recovers
exitBSub
       rts

Rob

[bigmac]

Hello Rob,

What is the Vdd level when you attempt to clear the low voltage warning?  Is your setting for bits LVDV:LWWV  within SPMSC2 register appropriate to your operating voltage?  Otherwise, I cannot see any reason why the LVWF flag should not be cleared.

Within the ISR, it may also be a good idea to re-write the LVDV:LVWV bit settings, just in case they might become corrupted over an extended period of time.

Regards,
Mac

[RobG]

Hi Mac,

Thanks. You woke me out of my mental blank. This application runs at 4.7 V. My intention is to use the low warning and reset levels but I was testing with the highest levels. I was puzzling over why once LVWF was set that even reset wouldn't clear it. The answer is simple. Hysteresis.

I'll take your advice and re-write SPMSC2 in the ISR.

Cheers and thanks again

Rob