CMPX - Compare the X Register Command

The CMPX command will compare the value currently stored in the X register with the argument.
The argument can be either a defined value (decimal or hex) such as #10 or #0x0a, or it can be a reference to a port or memory location.
The result of the comparison is used to make decisions in the task by setting/clearing the zero, carry, and minus flags.

Syntax

Basic Use
CMPX x Where x is the value or memory you want to compare to the X register.
The CMP comparison subtracts the value of its argument from the value in the X register.
While the result of the comparison is stored in the devices’s memory it does not change the value in the X register or accumulator.
This comparison value is used for branching commands. (BRZ, BNE, BCC, BPL, BMI, BRC)

List of flag interactions
Comparison	Zero Flag	Carry Flag	Minus Flag
Equal	Set	Cleared	Cleared
ACC Greater Than	Cleared	Cleared	Set if difference is greater than 128
ACC Less Than	Cleared	Set	Set

Advanced Use
CMPX Label,x
Where "Label" is the Label you want it to compare to offset by the value in the X register. As this compares the value in the X register to a value in an array offset by the same X register value it is not clear what a valid use case would be.

Arrays have an index of 4 so you must load a value of 5 into the X register to get the first value in the array. An array does not need to be in a task. It can be before or in between tasks in the task editor.

Examples

Example 1

Basic ways of using the CMPX command.

{
CMPX #11     //Compares the decimal value of 11 to the X register.
CMPX #0x0A   //Compares the Hex value of 10 to the X register.
CMPX ~2      //Compares whatever is stored in tilde memory ~2 to the X register.
CMPX ^35,1   //Compares lux level Hi byte to the X register.
CMPX ^10,0   //Compares keyboard port to the X register.
CMPX $10     //Compares value from persistent memory location 10 to the X register.
CMPX $Area4_State  //Compares value from persistent memory location named "Area4_State" to the X register.
CMPX #PrimaryArea  //Compares value of the constant named "PrimaryArea" to the X register.
CMPX @3      //Compares the opcode from the message buffer to the X register.
}

Example 2

This example shows how you can use the X register as a second accumulator.

{
...
DimDownLoop:
    LDA ~15          //Load what Bank we are in.
    CMP #0x06        //If we are already at 0% we aren't getting any Dimmer.
    BRZ DimDownEnd
    CMP #0x05
    BRZ Down10
    BRA Skip
    Down10:
    LDX #DimToOFF    //Load our Dim to off setting. 0=no, 1=yes.  We use the X Reg so the Accululator can hold bank.
    CMPX #0x00       //Is it a no?
    BRZ DimDownEnd   //If so end. If not continue.
    Skip:
    Inc              //Increase it by 1.
    STA ~15          //Store the new value back into the message buffer bank byte.
    Tx ~10,2,7       //Then we send it out onto the network.
    Delay(RampDelay)
    BRA DimDownLoop

    DimDownEnd:
        Null
...
}