pic16f77 acting goofy

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I will try to make this question as short as possible.  I'm making a
"quiz box" that displays the first two of any 20 players that buzz in.
I'm using a pic16f77.  The program scans 20 ports (buttons) and
displays the first two numbers (1-20) on four single digit 7-segment
LED displays via a display driver.  Also, a speaker buzzes after the
first player has buzzed in.  Everything works great except for this one
"little" bug.

When I first turn on the power, the displays get set to zero's and the
program starts scanning the buttons.  If I first push a button in the
teens (10-19) the first digit is always wrong.  For example, in stead
of displaying 12, it displays 32 or 72.  Next I push a button (1-9) and
it displays correctly.  If I reset the program and push the same
buttons in the same order, the problem occurs again.  However, if I
reset the program and first push a button (1-9), then push a button
(10-20), it displays correctly and every time thereafter until the
power switch is toggled off then on again.

The same thing happens when I turn the power on and first press a
button (1-9) then a button (10-19) - it displays incorrectly until I
reverse the order.  I push one (10-19) then one (1-9) and everything
works fine.

So, everytime I want to use it, I have to "intialize" it to get past
the bug before it will work right.  This problem is very perplexing.
The program debugs fine.  There is absolutely no reason for the mc to
be spitting out these goofy numbers.  Does anyone have any idea,
hardware or software, what could be causing this problem?  I hope this
wasn't too confusing.  Thanks in advance.

Steve


Re: pic16f77 acting goofy
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This problem is best fixed by single stepping in an emulator or in a
simulator.
I would be surprised if it was not a S/W problem.

--
Best Regards,
Ulf Samuelsson   ulf@a-t-m-e-l.com
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Re: pic16f77 acting goofy

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It sounds like you have forgotten to initialize a register. Namely, the one
that holds the most-significant digit. Check your initialization code.

Noel




Re: pic16f77 acting goofy
<snip>
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?!

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Well, there clearly must be a reason - it sounds very predictable:
you have just not found the reason, yet.

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  You have enough info in the interaction to start the debug process.
When a system is path dependent, but does have the ability to behave
correctly, it points to a software initialise problem.
  Look for different variable handling, in your 'works OK' path, from
the 'fails' path.
  It is good practice to clear all variable RAM on reset, in a 80c51
this takes 6 bytes of code - and can save a lot of other variable inits.
  You then code, so all 'safe defaults' are the 00 or FALSE values.

-jg


Re: pic16f77 acting goofy

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Zeroing ram is always a good idea at the start, but I find
it most useful in debugging because it makes a memory dump
easier to interpret.

I develop with RAM zeroed, and then verify operation with
ram set to 0FFH.  Variables that are not explicitly initialized
are verboten under all circumstances.

If you are having weird problems then setting memory to all 1's can
often make the source of the problem stand out like a sore thumb (or
stamp).

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
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Re: pic16f77 acting goofy
Wow, thanks for all the help and suggestions.  I'm using MPLAB IDE
v6.61 with MPLAB SIM.  I can step through the program and use the pin
stimulus feature to check the different scenarios.  The program seems
to work fine, storing all the correct values in each register.

I've declared two variables that keep track of the buttons pushed:
flag1 and flag2.  I intitialize these registers by

clrf flag1
clrf flag2

Is this sufficient?  In a later subroutine, those hex numbers get split
into dig1a, dig1b, dig2a, and dig2b to be sent to the display driver.
They are initialized the same way.  I'm not exactly sure what is meant
by the RAM.  Is that the block of general purpose registers used to
store all the variables?  If that's the case, then mine starts at 020H.
If I write all 0's (or 1's) to these registers, should I then run the
program to the point where it's messing up, and then do a memory dump
to see what each variable holds?

Jon, I would like to take a look at your box design, but there doesn't
seem to be a link with your message :=)

Steve


Re: pic16f77 acting goofy

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During your initialization, did you setup your PORTs to have the correct
default value? This is usually done just before a write to TRIS. It is just
as important as properly initializing your variables.


Noel



Re: pic16f77 acting goofy
Yes, I also clear all the ports before writing to the TRIS registers.
Steve


Re: pic16f77 acting goofy
On 17 Dec 2004 09:33:19 -0800, the renowned snipped-for-privacy@hotmail.com

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Assuming your program is written in assembler, this sounds like the
kind of PIC bug that results from forgetting a bank select instruction
somewhere.


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: pic16f77 acting goofy
My program is written in assembler and I've tried to be careful about
writing to the correct banks.  I do however get several messages like
this one:

Message[302] C:\PIC PROJECTS\QUIZ.ASM 34 : Register in operand not in
bank 0.  Ensure that bank bits are correct.

This is referring to me writing to the OPTION_REG which is in bank1.

bank1
movlw b'10000111'
movwf OPTION_REG        ; intitialize interrupts


bank1 macro
bsf STATUS, RP0
bcf STATUS, RP1
endm     

So, I think I'm writing to the banks correctly.


Re: pic16f77 acting goofy
On 17 Dec 2004 10:13:14 -0800, the renowned snipped-for-privacy@hotmail.com

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And you switch back to bank 0 after that in every case?


Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
snipped-for-privacy@interlog.com             Info for manufacturers: http://www.trexon.com
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Re: pic16f77 acting goofy
Yes I do, and I just stepped through the program again while monitoring
the STATUS bits.  After initializations, the bank bits stay in bank0
for the remainder of the program.


Re: pic16f77 acting goofy

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Steve,

I'm not trying to second-guess you but, is clearing the ports the correct
thing to do? In my own circuits, I usually have low-true scan signals. When
I do, I set those port bits to a 1.

HTH,

Noel





Re: pic16f77 acting goofy
Noel,

Do you mean that your inputs are active low?  Mine are active high.  I
have 1K pull-down resistors from each pin to ground.

Steve


Re: pic16f77 acting goofy

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Both the outputs, because I scan key matricies, and the inputs are
active-low. This is done for noise immunity and habit from two decades of
design with TTL-level circuit. Since mine are active-low, I initialize the
device with high (negated) outputs.

Your technique will work fine. I hope you didn't think I was being
remedial.

Noel



Re: pic16f77 acting goofy
I did something similar with an Atmel AT90S2313 processor.  Code works fine and
is in use, I believe.  Circuit schematics and box and source code etc. are all
right here if that helps, too.  Here's some of the header comments:

;   This program operates a Jeopardy or college-bowl kind of game device
;   where the first person to press a switch is selected, locking out the
;   others.  Eight contestants are supported, each by direct connection to
;   an input pin.  An LED lights up to indicate which switch (contestant)
;   is pressed first and the rest of the contestants are then locked out.
;   The buzzer emits a short burst, as well, to signal that a contestant
;   has pressed their button.

Not 20 buttons in this case, but extending it would be easy.  In any case, the
basic ideas in the code are there, too.

Jon

Re: pic16f77 acting goofy

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After re-reading your description, and in light of the rest of the thread,
it looks like your scanning and port initialization are correct. Perhaps
there is an uninitialized variable in the routine that converts the scanned
key to a displayed value.

You mentioned that if you press, say, key 19, you see key 39 or key 79. in
binary:
19: 0001 1001
39: 0011 1001
79: 0111 1001

Since I have not seen your conversion routines I cannot be sure but it
looks like a register used for the most-significant digit is not being
initialized.

Noel





Re: pic16f77 acting goofy
Noel,

Remedial is fine with me.  I'm open to improvement and I in no wise
consider myself an expert (competent? :=) )at any of this.

Now that I look back over my program I can see that I don't initialize
dig1a or dig1b (I've changed things around a lot while
troubleshooting).  My thinking there was that those registers get
rewritten anyway before being used to send data to the display.  Here
is my conversion routine:


___movf flag1,0
___movwf temp               ; move flag1 to temp for safe keeping
___movlw .10             ; store 10 in W
___subwf temp,0          ; subtract 10 (W) from temp (flag1)
___btfsc STATUS,C        ; check if flag1<10
___goto aGreater10       ; no (C=0)
___movf flag1,0          ; yes (C=1), move flag1 to W
___movwf dig1b           ; we have dig1b
___clrf dig1a            ; we have dig1a (0)
___goto Output1
aGreater10
___btfsc flag1,4         ; check if flag120% (10100)
___btfss flag1,2
___goto aNot20
___movlw .2
___movwf dig1a           ; we have dig1a (2)
___clrf dig1b               ; we have dig1b (0)
___goto Output1
aNot20
___movf flag1,0
___movwf temp               ; move flag1 to temp for safe keeping
___movlw .10               ; store 10 in W
___subwf temp,0          ; subtract 10 (W) from temp
___movwf dig1b           ; we have dig1b
___bsf dig1a,0           ; we have dig1a (1)
Output1
"
sends data to the display
"

Since I only have 20 buttons, the only possibilities for dig1a is
either 0, 1, or 2 - not 3, 5, 7, or "F" like I'm getting.  How
(generally) can I read or write to RAM in order to check the
initializations like some of the earlier posts were referring to?
Steve


Re: pic16f77 acting goofy

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clearing dig1a in initialization may help. You may also want to change:
bsf dig1a,0
to:
movlw 0x01
movwf dig1a

I don't see dig1a being in the case of a key in the 10-19 range.

Just an educated guess,

Noel



Re: pic16f77 acting goofy
Noel,

"I don't see dig1a being in the case of a key in the 10-19 range."

Let me be more clear.  If, for example, button 15 is pushed, flag1
stores the value 15 (0F).  Then the conversion routine splits that up
so that dig1a stores a 1 and dig1b stores a 5.  Is that what you were
getting at?

By the way, these are good suggestions which I will try early next week
as I don't have my box with me right now.

Steve


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