From: Ken Horton <xxxxxxxxx@ntlworld.com>
To: 'John Becker' <john.becker@wimborne.co.uk>
Subject: Canute Tide Predictor
Date: 10 November 2003 08:01

John

You possibly recall our correspondence at the beginning of the year (below)
on the Canute Tide Predictor and a problem with incorrect tide times.

The unit has been brought back from Portugal for me to look at. I have made
the following changes:

GETHRS: clrf STORE2
GTHRS2: incf STORE2,F    ;get hours value (divide by 60)
        movlw 60
        subwf STORE0,F
        btfsc STATUS,C
        goto GTHRS2
        movlw 1
        subwf STORE1,F
        btfsc STATUS,C
        goto GTHRS2
        decf STORE2,F
        movlw 60
        addwf STORE0,F
;        movlw 24
;        xorwf STORE2,W
;        btfsc STATUS,Z
;        clrf STORE2
;        return
        movlw 232       ; * Ken kfh
        addwf STORE2,w  ; * Ken kfh
        BTFSS STATUS,C  ; * Ken kfh
        return          ; * Ken kfh
        movwf STORE2    ; * Ken kfh
        return          ; * Ken kfh



GETSIN: movf INDF,W     ;BYTE2 ;is angle >= 90?
GS1:
        movwf STORE1
        addlw 166
        btfss STATUS,C
        goto GS2        ;no
        sublw 90        ;yes, now subtract answer from 90
;        movwf STORE1    ;and store new value
	goto GS1        ; * Ken kfh
GS2:    return

There is no evidence that GETSIN is going wrong, but I thought it was a wise
precaution!


I have also made the following change to the graph as it was 'sticking' at
one end when the duration of the low and high tides were significantly
different.

CHKHI:  movf CLKHRS,W     ;are HRS = high tide hours?
        xorwf NXTHI1,W
        btfss STATUS,Z
        goto CHKLO
        movf CLKMIN,W     ;are MINS = high tide mins?
        xorwf NXTHI0,W
        btfss STATUS,Z
        goto CHKLO
        clrf TIDEUP
        movlw 0xBC        ; * Ken kfh
        movwf TIDE0       ; * Ken kfh
        movlw 1           ; * Ken kfh
        movwf TIDE1       ; * Ken kfh
        call CLRLN1       ; * Ken kfh
        goto GF0

CHKLO:  movf CLKHRS,W     ;are HRS = low tide hours?
        xorwf NXTLO1,W
        btfss STATUS,Z
        goto GF3          ;no
        movf CLKMIN,W     ;yes, are MINS = low tide mins?
        xorwf NXTLO0,W
        btfss STATUS,Z
        goto GF3          ;no
        bsf TIDEUP,0      ;yes
        clrf TIDE0        ; * Ken kfh
        clrf TIDE1        ; * Ken kfh
        call CLRLN1       ; * Ken kfh
        movlw 15
        call LCDPX1
        movlw '>'
        call LCDOUT
        movlw 12           ;show time of next high tide
        call LCDPX2
        movf NXTHI1,W
        movwf NOWHI1
        call LCDHEX
        movf NXTHI0,W
        movwf NOWHI0
        call LCDHEX
        goto GF3


Regards


Ken


[...]

> >
> >
> > ----- Original Message -----
> > From: Fay Kenward <fay.kenward@wimborne.co.uk>
> > To: John Becker <john.becker@wimborne.co.uk>
> > Sent: Monday, October 28, 2002 9:34 AM
> > Subject: FW: Canute Tide Predictor
> >
> >[...]
> > >
> > >
> > > Dear Mr Becker
> > >
> > > When the article for the Canute Tide Predictor was published, I
> > > built one, and this is in continual use on an ocean going boat in
> > > Portugal.
> > >
> > > I understand that every so often, the clock goes wrong displaying
> > > 25:00 hours before locking-up. Unfortunately, I am unable to give
> > > you the precise details of the error as I have not had chance to
> > > witness the symptoms first hand.
> > >
> > > Are you aware of this error, and if so if there a fix for it?
> > >
> > >
> > > Regards
> > >
> > > Kenneth Horton