Although J is automatically applied to all memory reference and I/O instructions inside a MultiTrack task (unless you use NoJ:), there may be occasions when the automatic behaviour is not what you need. The BranchJ instructions gives you an open ended way of forcing exactly what you need to happen.

BranchJ works in a similar way to the other Branch instructions (Branch, BranchM, BranchR). It gives you an “n-way branch” depending on the value of J.

Example:

In this (really exciting! : -) version of our on/off light switch, the order of the outputs is reversed relative to the inputs, i.e. input 0 controls output 3, 1 controls 2, 2 controls 3 and 3 controls 0.

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        LaunchTask      Toggle,0
        LaunchTask      Toggle,1
        LaunchTask      Toggle,2
        LaunchTask      Toggle,3
        RunTasksForever
Toggle:
        WaitOnK         0
        GoSub           Reverse
        iOn             0
        WaitOnK         0
        GoSub           Reverse
        iOff            0
        GoTo            Toggle

Reverse:
        LoadI           3
        BranchJ
        Target          J0
        Target          J1
        Target          J2
        Target          J3

J3:
       DecI
J2:
       DecI
J1:
       DecI
J0:
       Return

Exercise 1:

Analyze how the program works.

Exercise 2:

What happens if you change the iOn and iOff instructions with IasJ:On and IasJ:Off respectively?

Exercise 3:

Rewrite the Reverse subroutine for the following mapping, not using a chain of DecI instructions. Do use the BranchJ instruction.: