Binary assignment syntax - confused?

[mister_e]

     Bit #  76543210
TRISIO =   %01010101

if you want to set few bits without altering the other, you may need to set them manually one after the other or use bitwise OR.

let's say you want to change bit 0,2,4,6 of OPTION_REG which you already set to %00000000, then all you need to do is to use
OPTION_REG=OPTION_REG | %01010101

You can refer to section 4.17 and see the following
http://www.learn-c.com/boolean.htm

HTH