Why won't this compile? cc = a ^ b

basicstampede · 2008-09-03 00:25

Hello.·

I want to monitor two pins.

When the two pins are dissimilar, then I want to increase a counter by 1.

Here is my code.· It won't compile.· The error message says "unknown command LET".· What is this?

' =========================================================================
'
'·· File......
'·· Purpose...
'·· Author....
'·· E-mail....
'·· Started...
'·· Updated...
'
' =========================================================================

'

' Program Description
'

'

' Conditional Compilation Symbols
'

'

' Device Settings
'

DEVICE········· SX28, OSC4MHZ, TURBO, STACKX, OPTIONX, BOR42
FREQ··········· 4_000_000

'

' I/O Pins
'

Pin1 PIN RA.0 INPUT
Pin2 PIN RA.2 INPUT
'

' Constants
'

'

' Variables
'

·a VAR bit
·b VAR bit
·cc VAR bit
' =========================================================================
' INTERRUPT
' =========================================================================
'ISR_Start:
· ' ISR code here
'ISR_Exit:
· 'RETURNINT ' {cycles}································

' =========================================================================
· PROGRAM Start
' =========================================================================

'

' Subroutine / Function Declarations
'

'

' Program Code
'

Start:
· a = Pin1
· b = Pin2
·
· cc = a ^ b
· IF cc = 1 THEN
··· counter = counter + 1
· ENDIF
Main:
· GOTO Main

'

' Subroutine / Function Code
'

'

' User Data
'

·

Bean · 2008-09-03 00:29

XOR doesn't work with bit variables.

Forget about cc altogether and just use "IF a <> b THEN".

Bean

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·

JonnyMac · 2008-09-03 00:33

Funny how the simplest solutions are usually the most elegant; that even matches the requirement statement: "When the two pins are dissimilar...."

basicstampede · 2008-09-03 00:39

Thanks Bean. That is good to know about XOR.

basicstampede · 2008-09-03 00:54

JohnnyMac, actually, my code was something like this:

Main:
SHOW_TIME
oldpin = newpin
newpin = TicPin
'result = oldpin ^ newpin 'XOR does not work on Bit

IF oldpin <> newpin THEN 'Forget about result, just compare oldpin v. newpin
counter = counter + 1
IF counter = 2 THEN
counter = 0
UPDATE_TIME
ELSE

I was actually monitoring 1 pin to see if it changed. So I saved it as oldpin, then got a new reading as newpin and tried to do an XOR.
Anyway, now thinking again, I agree that I should have just directly compared it instead of XORing it.
But I learned that XOR does not work on Bit variables.
Thanks for all your help.

JonnyMac · 2008-09-03 01:02

You will find new strategies moving from the BASIC Stamp to the SX; sometimes they seem like a lot more work, but what you really don't see is how much work the BASIC Stamp actually does for us, though you begin to get an idea once you start coding the SX.

I'd still like to see your whole program or what you're attempting to convert; sometimes fragments have no context and one would approach them differently given a "big picture" view.

[noparse][[/noparse]Edit] Looking at your code, I think this is more efficient and accomplishes the same thing:

Main:
  SHOW_TIME
  IF TicPin <> oldPIN THEN
    oldPin = TicPin
    INC counter
    IF counter.0 = 1 THEN
      UPDATE_TIME
    ENDIF
  ENDIF

... basically it calls the UPDATE_TIME subroutine on every other change of TicPin.

And, just for grins, here's another way to do it. Let's say you want to call UPDATE_TIME when you have a 0 to 1 transition on TicPin; here's a possible solution:

Main:
  SHOW_TIME
  ticCheck = ticCheck << 1                      ' last check to BIT1
  ticCheck = ticCheck & %11                     ' clear all but bits 1 and 0
  ticCheck.0 = TicPin                           ' sample to BIT0

  IF tixCheck = %01 THEN                        ' if last low, new high
    UPDATE_TIME                                 '   update
  ENDIF

This second segment of code uses just one byte versus one byte + one bit, or one byte + two bits with your original code.

Post Edited (JonnyMac) : 9/3/2008 1:29:02 AM GMT

basicstampede · 2008-09-03 18:20

Jonny Mac, below, please see my entire code. Thanks for all your help.

' =========================================================================
'
' File...... Stampworks10
' Purpose... Stampworks 10 in SX/B
' Author.... C.M.
' E-mail....
' Started... Sept. 1, 2008
' Updated...
'
' =========================================================================

'

' Program Description
'

' 8 digit LED
' takes input square voltage in TicPin (RB.0) and uses this as timing signal
' displays time in four 8 segment LEDs
' uses time multiplexing and persistence of vision

'

' Conditional Compilation Symbols
'

'

' Device Settings
'

DEVICE SX28, OSC4MHZ, TURBO, STACKX, OPTIONX, BOR42
FREQ 4_000_000

'

' I/O Pins
'

Segs PIN RC OUTPUT
TicPin PIN RB.0 INPUT
DigSel PIN RA OUTPUT

'

' Constants
'

Blank CON 0
Dig0 CON %1111 'all digits off
Dig1 CON %0111 'tens minutes digit
Dig2 CON %1011 'ones minutes digit
Dig3 CON %1101 'tens seconds digit
Dig4 CON %1110 'ones seconds digit

'

' Variables
'

'idx VAR Byte
counter VAR Byte
sec VAR Byte

seconds VAR Byte
minutes VAR Byte

sec_ones VAR Byte
sec_tens VAR Byte
min_ones VAR Byte
min_tens VAR Byte

digit VAR Byte
digitvalue VAR Byte
value VAR Byte
pinstatus VAR Byte
time VAR Byte

oldpin VAR Byte
newpin VAR Byte
result VAR Byte

' =========================================================================
' INTERRUPT
' =========================================================================

'ISR_Start:
' ISR code here

'ISR_Exit:
'RETURNINT ' {cycles}

' =========================================================================
PROGRAM Start
' =========================================================================

'

' Subroutine / Function Declarations
'

SHOW_TIME SUB 0
UPDATE_TIME SUB 0

'

' Program Code
'

Start:

counter = 0
sec = 0
digit = 0
DigSel = Dig0

newpin = TicPin

Main:
SHOW_TIME
oldpin = newpin
newpin = TicPin
result = oldpin ^ newpin

IF result <> 0 THEN
counter = counter + 1
IF counter = 2 THEN
counter = 0
UPDATE_TIME
ELSE
'only changed 1 time
'oldpin = newpin ' try adding more code here
ENDIF
ELSE
'oldpin = newpin ' try adding more code here
ENDIF

WATCH sec
WATCH seconds
WATCH minutes
WATCH sec_ones
WATCH sec_tens
WATCH min_ones
WATCH min_tens
WATCH value
WATCH digitvalue
WATCH oldpin
WATCH newpin
BREAK

GOTO Main

'

' Subroutine / Function Code
'

SUB SHOW_TIME
'Segs = Blank ' try activating this
digSel = Dig4
READ DecDig+sec_ones, Segs
PAUSE 1
digSel = Dig3
READ DecDig+sec_tens, Segs
PAUSE 1
digSel = Dig2
READ DecDig+min_ones, Segs
PAUSE 1
digSel = Dig1
READ DecDig+min_tens, Segs
PAUSE 1
DigSel = Dig0 'need this? try eliminating this.
'
ENDSUB

SUB UPDATE_TIME
sec = sec + 1

IF sec=60 THEN
sec = 0
sec_tens = 0
sec_ones = 0
min_ones = min_ones + 1
IF min_ones = 10 THEN
min_ones = 0
min_tens = min_tens + 1
IF min_tens = 9 THEN
min_tens = 0
ENDIF
ENDIF
ELSE
sec_tens = sec / 10
sec_ones = sec // 10
ENDIF
ENDSUB

'

'

' User Data
'

DecDig:
DATA %01111110 '0
DATA %00110000 '1
DATA %01101101 '2
DATA %01111001 '3
DATA %00110011 '4
DATA %01011011 '5
DATA %01011111 '6
DATA %01110000 '7
DATA %01111111 '8
DATA %01111011 '9
DATA %01110111 'A
DATA %00011111 'b
DATA %01001110 'C
DATA %00111101 'd
DATA %01001111 'E
DATA %01000111 'F

JonnyMac · 2008-09-03 20:49

I wrote StampWorks, so I recognize that. Keep in mind, though, that what we're forced to do with BS2 we don't always have to do with the SX; in many cases direct translations simply cripple the capabilities of the SX.

I've translated the program similar to what you're doing, but that program in StampWorks was to demonstrate the process of multiplexing, and was never intended to be a practical application. The SX has interrupts and that's the better way to go for this type of application. See the help file for a clock/time example using interrupts in SX/B. In the mean time you may learn a few tricks about SX/B from the attached program.

For example: you should encapsulate high-level functions like PAUSE into a subroutine so that they just get compiled once -- this will save code space. You might want to go back and read all my Nuts & Volts articles that use the SX. Since I have to explain the project code it should be fairly educational, especially those articles over the last year or so. You can get them from the Parallax web site.

Why won't this compile? cc = a ^ b

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