12f675_fuse_about_to_blow!

[LEDave]

Calculate checksum by adding 2 data bytes together

CheckSum = DAT_IN1 + DAT_IN2

So the CheckSum = (%10101011 * 2 BYTES) if SW1 ( GPIO.3) was pressed.

or (%10101101 * 2 BYTES) if SW2 (GPIO.4) was pressed.

Plus we should have the already have a calculated CHK_SUM that was sent.

So:

CHK_SUM   VAR BYTE  ' Holds checksum received

And:

CheckSum  VAR BYTE  ' Computed checksum of all bytes received

Therefore:

IF CheckSum != CHK_SUM THEN MAIN ' Failed checksum, return

If Checksum (!) is not = CHK_SUM then go back to MAIN the checksum has failed.

The same with:

IF (DAT_IN1) != (DAT_IN2) THEN MAIN ' Failed data comparison, return

The DAT_IN BYTES must also be equal, if not then back to MAIN:

If however everything matches then continue to MATCH..........

How does this look?

Dave

[LEDave]

Another question:

wsave   VAR	BYTE $5F system	   ' Saves W

Bruce's code talks of Bank0 system. Am I correct in saying that BYTE $5F system is setting bit.5 of the STATUS REG to 0 which is selecting Bank0 ($5f = %1011111).

So to change from Bank0 to Bank1 would be %1111111

Also:

movwf  wsave	 ; Save W

So these commands mean Move the contents of the W REG to the address of wsave.

Mm, not really sure about this............(more reading to do).

Dave


Dave

[mackrackit]

The DAT_IN BYTES must also be equal, if not then back to MAIN:

If however everything matches then continue to MATCH..........

How does this look?

I think you got that part down.

Bruce's code talks of Bank0 system. Am I correct in saying that BYTE $5F system is setting bit.5 of the STATUS REG to 0 which is selecting Bank0 ($5f = %1011111).

So to change from Bank0 to Bank1 would be %1111111

Like I said, ASM is not my strong point. Not sure I have a strong point...
Below tells how to change banks, I think.

If the PICmicro has more than 2K of code space, an interrupt stub is automatically added that saves the W, STATUS and PCLATH registers into the variables wsave, ssave and psave, before going to your interrupt handler. Storage for these variables must be allocated in the BASIC program:

	wsave  var	        byte $20 system
	wsave1 var	byte $a0 system		' If device has RAM in bank1
	wsave2 var	byte $120 system	' If device has RAM in bank2
	wsave3 var	byte $1a0 system	' If device has RAM in bank3
	ssave    var	byte bank0 system
	psave    var	byte bank0 system

movwf  wsave	 ; Save W

So these commands mean Move the contents of the W REG to the address of wsave.

Yes.
Also notice that all of the data is restored in the opposite sequence it was saved.

If I am giving wrong ASM info , somebody please jump in and correct me!

[LEDave]

Hi mackrackit,

Not sure I have a strong point...

Hey, you put up with me, so patience is one of them

And don't forget it was trying to turn an LED on using ASM that after a near breakdown put me onto PBP

I'll go onto MATCH & DECODE tomorrow, slowly getting there (slowly).

Dave

[LEDave]

It still doesn't take much to stump me I'm afraid........

 MATCH = MATCH + 1        ' We have a match so increment match count
    IF MATCH = 2 THEN DECODE ' Everything matched twice, we're good
    GOTO Main                ' Else do it all over

When the Timer was set up for a 65ms reset we had:

MATCH = 0           ' Clear match count

Then the SYNCH_BYTE & DATA etc arrived and everything was good giving:

MATCH = MATCH + 1        ' We have a match so increment match count

So to my mind that makes MATCH = 0 +1 ie 1.

But then we have:

 IF MATCH = 2 THEN DECODE ' Everything matched twice, we're good

So either the data arrives twice within the 65ms time period to move onto DECODE or my understanding of MATCH = MATCH + 1 is wrong.

Help!

Dave

[mackrackit]

So either the data arrives twice within the 65ms time period to move onto DECODE or my understanding of MATCH = MATCH + 1 is wrong.

Not within the 65ms but just twice. MATCH does not get set to zero until DECODE is reached.
One good set of data could arrive then many not-goods, then one more good THEN DECODE.

Being this came from Bruce it is hard for me to question it but....
Here is what I think it should be

    ' Test new checksum against one received in CHK_SUM
    IF CheckSum != CHK_SUM THEN MAIN ' Failed checksum, return
    MATCH = MATCH + 1        ' We have a match so increment match count

    ' Test data bytes for match
    IF (DAT_IN1) != (DAT_IN2) THEN MAIN ' Failed data comparison, return
    MATCH = MATCH + 1        ' We have a match so increment match count

    IF MATCH = 2 THEN DECODE ' Everything matched twice, we're good
    GOTO Main                ' Else do it all over

[LEDave]

Far more intuitive for a newbie your way mackrackit. I would have been stuck in a loop looking for a second MATCH until my watchdog timer kicked in (that's not to say Bruce's program isn't pure genius from where I'm sitting).

I'm thinking that if one MATCH had occurred but was followed by bad data, then the ASM :

clrf   MATCH         ; Clear match variable

would reset the single MATCH to zero after 65ms?

Onto DECODE then.

Dave