Addressing bits in loop counters

[Summertown]

Chips 28X1 & 18M2

I am trying to set/clear some bits. At the moment I am setting/clearing separately e.g.

Bit1 = 0
Bit2 = 0
and so on

What would be easier would be to be able to do something like;
Counter1 being a register B5 and above
For counter1 = 3 to 11
BitCounter1 = 0
next counter1

Similarly I need to interrogate the bits

For counter1 = 3 to 11
If BitCounter1 =1 then........
Next Counter1

Any suggestions?

Thanks

 

[HertzHog]

The bits form part of the overlapping byte and word so you can clear them all by setting the byte to zero.

 

[Summertown]

Dear HertzHog,
Thanks for being quick of the mark with a reply.

I am aware that the 32 bits double up as B0 to B3 in both the mentioned chips.

Maybe my question wasn't clear enough.
I need to set & interrogate, and set a number of bits (I used 3 to 11 in the above question) the bits may/may not be multiples of bytes, as you implied.

If I was examining Bytes I can use indirect addressing. Is indirect addressing available for bytes?

Cheers

 

[Summertown]

last line should be:
If I was examining Bytes I can use indirect addressing. Is indirect addressing available for bits?

Sorry about the typo

 

[nick12ab]

There's no 'bitpointer' for bits like there's a byte pointer for bytes.

Does using a bit mask help?

b1 = b1 AND %01010101

In that example, bits 9,11,13 and 15 will be cleared and the other bits in that byte are retained.

 

[pvdven777]

On the X2 parts couldn't you just use setbit/clearbit ?
Example :
setbit b6, 0 ' setbit bytevar, countervar

Otherwise you can manipulate bits by maths.
I am using this following solution in a loop within a piece of code which I intend to post in a day or so :
Sendcode = Sendcode + 1 ' Set least sigificant bit of variable.

Reading back individual bits can be done using a mask :

for counter = 1 to bits ' Count up to number of bits to send
mask = var_out & 128 ' Mask MSB
if mask = 0 then low testvar else ' work out if bit is high or low
high testvar
endif
next counter ' Loop to check out next bit

I've got 128 hardcoded to get the most significant byte. Then on each loop (not shown in sample code) I shift the byte value to get the next bit. You could also use a variable instead to point to a certain bit on each loop. (This is actually a modified piece of sample code from the bitbang example in the picaxe manual)

Hope that helps !

Patrick

 

[hippy]

To determine a bit value using an index you can do this -

LookUp index, ( bit0, bit1, bit2, ... , bit30, bit31 ), bitValue

There's no simple equivalent for setting or manipulating bits, but you can use LOOKUP to convert index to a bit mask and apply that, for bits 0 to 15 -

Lookup index, ( $1, $2, $4, $8, $10, $20, ... , $4000, $8000 ), bitMask
w0 = w0 | bitMask

For 32 bits you could use ...

Lookup index, ( $1 ... $8000, $1 .. $8000 ), bitMask
If index <= 15 Then
w0 = w0 | bitMask
Else
w1 = w1 | bitMask
End If

SET : w0 = w0 | bitMask
CLR : w0 = bitMask ^ $FFFF & w0
TOG : w0 = w0 ^ bitMask
GET : bitValue = w0 & bitMask Max 1

 

[Summertown]

Hi Hippy,
The mask method you suggest is the one I am using, it works well but is messy to compose code for.

Thanks for the verification.
Gonzo aka Summertown