LoadBit

Source: Positron8 Compiler User Manual, PDF page 336

Syntax

LoadBit Variable, Index, Value

Overview

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

Parameters

Variable is a user defined variable, of type Byte, Word, Long, or Dword. Index is a constant, variable, or expression that points to the bit within Variable that requires accessing. Value is a constant, variable, or expression that will be placed into the bit of interest. Values greater than 1 will set the bit.

Example

 ' Copy variable ExVar bit by bit into variable PT_Var
  Device = 16F1829
  Declare Xtal = 4
                             ' Tell the compiler the device is operating at 4MHz
  Dim ExVar as Word
  Dim Index as Byte
  Dim Value as Byte
  Dim PT_Var as Word
  Do
     PT_Var = 0b0000000000000000
     ExVar = 0b1011011000110111
     Cls
     For Index = 0 to 15
                                       ' Create a loop for 16 bits
       Value = GetBit ExVar, Index
                                       ' Examine each bit of variable ExVar
       LoadBit PT_Var, Index, Value  ' Set or Clear each bit of PT_Var
       Print At 1, 1, Bin16 ExVar
                                       ' Display the original variable
       Print At 2, 1, Bin16 PT_Var
                                       ' Display the copied variable
       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 or set 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 LoadBit command makes this task extremely simple by taking advantage of the indirect method using FSR, and INDF, 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. i.e. PORTA.1 = 0

To set a known constant bit of a variable or register, then access the bit directly using Port.n. i.e. PORTA.1 = 1

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