ClearBit

Syntax

ClearBit Variable, Index

Overview

Clear a bit of a variable or register using a variable index to the bit of interest.

Parameters

Variable is a user defined variable. Index is a constant, variable, or expression that points to the bit within Variable that requires clearing.

Example

' Clear then Set each bit of variable ExVar
  Device = 16F1829
  Declare Xtal = 4
  Dim ExVar as Byte
  Dim Index as Byte
  Cls
  ExVar = 0b11111111
  Do
                                     ' Create an infinite loop
     For Index = 0 to 7
                                     ' Create a loop for 8 bits
       ClearBit ExVar,Index
                                     ' Clear each bit of ExVar
       Print At 1,1,Bin8 ExVar
                                     ' Display the binary result
       DelayMs 100
                                     ' Slow things down to see what's happening
     Next
                                     ' Close the loop
     For Index = 7 to 0 Step -1
                                     ' Create a loop for 8 bits
       SetBit ExVar,Index
                                     ' Set each bit of ExVar
       Print At 1,1,Bin8 ExVar
                                     ' Display the binary result
       DelayMs 100
                                     ' Slow things down to see what's happening
     Next
                                     ' Close the loop
  Loop
                                     ' Do it forever

Notes

There are many ways to clear a bit within a variable, however, each method requires a certain amount of manipulation, either with rotates, or alternatively, the use of indirect addressing using the FSR, and INDF registers. Each method has its merits, but requires a certain amount of knowledge to accomplish the task correctly. The ClearBit command makes this task extremely simple using a register rotate method, however, this is not necessarily the quickest method, or the smallest, but it is the easiest. For speed and size optimisation, there is no shortcut to experience.

To Clear a known constant bit of a variable or register, then access the bit directly using Port.n.

PORTA.1 = 0

or

Var1.4 = 0

If a Port is targeted by ClearBit, the TRIS register is not affected.

See also : GetBit, LoadBit, SetBit.