How to: Inverting Bits

The guide demonstrates how to create an expression that will invert the bits of a given tag. Before starting, create a local Modbus device, a tag with the name source_tag and data format WORD (16-bit unsigned integer).

Open Monokot Server Administrator, double-click Scripts on the Server Explorer pane and go to the Modules tab. Click the New Module button and name the module BitsOp. Insert the following code into the code editor:

function bit_test(num, bit){
    return ((num>>bit) % 2 != 0)
}

function bit_set(num, bit){
    return num | 1<<bit;
}

function bit_clear(num, bit){
    return num & ~(1<<bit);
}

function bit_toggle(num, bit){
    return bit_test(num, bit) ? bit_clear(num, bit) : bit_set(num, bit);
}

Press Ctrl + Enter to apply the change in the code editor.

Thus, the following functions are defined in the BitsOp module:

• bit_test: returns the state (true or false) of the bit number bit from the number num

• bit_set: sets the bit number bit of the specified number num to true and returns the resulting number

• bit_clear: resets the bit number bit of the specified number num to false and returns the resulting number

• bit_toggle: inverts the bit number bit of the specified number num and returns the resulting number

Go to the Expressions tab and click the New Expression button. For the expression that appeared, set the name Inverse and specify the data type WORD (16-bit unsigned integer). Insert the following code into the expression code editor:

const NUMBER_OF_BIT = 16;

var value = context.data['source_tag_trig'].state.value;

for (var i = 0; i < NUMBER_OF_BIT; i++)
  value = bit_toggle(value, i);

return value;

Press Ctrl + Enter to apply the change in the code editor.

While in the code editor you can check the syntax by pressing the F9 key

Go to the Triggers tab and click Add Data.... Select the previously created tag (source_tag) as the data source for the trigger. Enter source_tag_trig as the name (key) of the trigger.

Go to the Imports tab and click the checkbox of the BitsOp module.

In order for the changes to take effect on the server, click the Sync button. If you switch to Go Online mode, you will see a picture similar to the following (in my case, the number 21845 is inverted).