simple SX/B question

Alex Hunter

Hello, i'm new to the SX, and i have a simple question that i can't figure out.

I would like to use code similar to the following:

for idx = 0 to 7
     HIGH RA.idx
next

I would like to use a variable to identify a pin. But this code doesn't work. Is there some way i can get something like this to work, without using if-then statements?

Thanks,
Alex Hunter

John Couture

Edited after I realized I goofed on my answer.

My apologies gang.· I just realized that my answer was so far off that it was flat out wrong ... thus I deleted it so that it doesn't get used.· Bean gave much better advice in the next message.

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John J. Couture

San Diego Miramar College

Post Edited (John Couture) : 8/3/2006 5:36:29 AM GMT

Bean

Alex,
· You cannot use a variable for the bit position. This is because of the way the SX instructions are formed.
· Probably the easiest way is to do this:

OUTPUT RB             ' Make all bits of RB outputs
FOR idx = 0 to 7
  tempByte = 1 << idx ' Get a 1 in the position to turn on
  RB = RB OR tempByte ' Make pin high
NEXT

Bean.


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Cheap 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com

"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
·

John Bond

Hey Bean

I found your trick the hard way last week. I thought I was real stupid finding no other way but by using the OR function. it makes me feel a little better seeing you're using it.

John Bond

Bean

Here is a way to do it without needing the tempByte variable.

idx VAR Byte
 
OUTPUT RB             ' Make all bits of RB outputs
idx = 1
DO
  RB = RB OR idx
  idx = idx << 1
LOOP UNTIL idx = 0 ' 128 << 1 = 0 for byte variables
 

Bean.

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Cheap 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com

"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
·

Alex Hunter

thanks bean, that is very helpful.

Yendor

I had a similar situation.

Using the 'Bean' strategy, is there a similar way we can access the individual bits using an index, instead of shifting a byte?

For example if I wanted to test individual bits of a byte:

idx VAR BYTE
mybyte VAR BYTE

FOR idx = 0 TO 7
IF mybyte.idx = 1 THEN ' which won't work
'do somethin'
ENDIF
NEXT

An array of bits was another idea, but the compiler didn't like it.

Kinda like mybyte.LowBit(idx)) for the BS2 code.

Thanks!

Bean

Sure you can do this:

idx VAR BYTE
mybyte VAR BYTE
tempByte VAR Byte

FOR idx = 0 TO 7
  tempByte = 1 << idx
  tempByte = tempByte AND myByte
  IF tempByte <> 0 THEN
    'do somethin'
  ENDIF
NEXT

Bean

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Cheap 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com

"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
·

Yendor

Thanks Bean.

Ah yes, being tricky with bytes! I was thinking that there were some functions using or accessing bits like in PBASIC other than mybyte.1.

many thanks!

Bean

You can use __PARAM1 for those tempByte variables too. That way it doesn't require extra variable space.

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Cheap 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com

"You're braver than you believe, stronger than you seem, and smarter than you think" Christopher Robin to Pooh
·

Yendor

Nice tip. However, I'm probably a way's away from touching any limitations in RAM.