On Thu, Jun 18, 1998 at 10:08:48AM -0500, [EMAIL PROTECTED] wrote:
>
> I need to set bits 0,1,4,5,6,7,11 for port 0x201. I have NO IDEA how
> to calculate the bitmask! Obviously I need to learn this stuff so were
> can I read up on this.
Read any book on analysis for undergraduates.
The base number of the decimal system is 10. For example, 9378 can be
read as
9*10^3 + 3*10^2 + 7*10^1 + 8*10^0
Note that 10^0=1, 10^1=10 and so on.
For computers, the base 10 is not commonly used, better
are 2, 8 and 16.
The bits are really the digits of numbers with base 2.
You want the number 100011110011
^ ^
bit 11 bit 0
= 1*2^11+1*2^7+1*2^6+1*2^5+1*2^4+1*2^1+1*2^0
= 2048+127+64+32+16+2+1 = (left as an exercise for the reader)
But it is easier, because you have to supply the bit mask as
a hexadecimal number (0x????), so you can take four base2-digits
and form a hexadecimal digit (base 16=2^4)
(you have to start from the back)
0011 (base2) = 3 (base 10) = 3 (base 16)
1111 (base2) =15 (base 10) = f (base 16)
1000 (base2) = 8 (base 10) = 8 (base 16)
So: 100011110011 (base2) = 0x08f3
Note that the hexadecimalsystem has by convention the digits
0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f
Marcus
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