Free Signals API

This is the Free Signals API for PLC specific tasks. It extends the Lua base library.

Returns handle to a digital input. connector_index is the numeric ID of the IO connector (Currently only Modbus couplers are supported). input_index is the numeric ID of the digital input on the coupler.

Example:

my_button = plc.DI(0,0)

Returns the current state of the digital input as a boolean value.

Returns a string representation of the digital input with its address and the current state.

Pass a function to be called when the input switches from low to high.

Example:

my_button:on_rise(
   function() print("my_button pressed") end
)

Pass a function to be called when the input switches from high to low.

Example:

my_button:on_fall(
   function() print("my_button released") end
)

Pass a function to be called when the input changes its state from low to high or from high to low.

Example:

my_button:on_rise(
   function(self) print("my_button changed: "..self.tostring()) end
)

Returns handle to an analog input. connector_index is the numeric ID of the IO connector (Currently only Modbus couplers are supported). input_index is the numeric ID of the analog input on the coupler.

Example:

my_ai = plc.AI(0,0)

Returns the current value of the analog input as a Lua number.

The value is passed „as is“ from the bus coupler. No conversion takes place.

Returns a string representation of the analog input with its address and the current value.

Pass a function to be called when the input changes its value.

Example:

my_ai:on_change(
   function(self) print("my_ai changed: "..self.tostring()) end
)

Note that it is possible to set a threshold for what is recognized as a value change in the variable ai_tresh in the config file of each IO connector.

Returns handle to a digital output. connector_index is the numeric ID of the IO connector (Currently only Modbus couplers are supported). output_index is the numeric ID of the digital output on the coupler.

Example:

my_lamp = plc.DO(0,0)

Returns the current state of the digital output as a boolean value.

Returns a string representation of the digital output with its address and the current state.

Sets the digital output to the passed value converted to a boolean.

You can pass anything as value. Converion to boolean takes place according to the Lua rules: Both nil and false make a condition false; any other value makes it true.

Inverts the digital output.

Returns handle to a analog output. connector_index is the numeric ID of the IO connector (Currently only Modbus couplers are supported). output_index is the numeric ID of the analog output on the coupler.

Example:

my_ao = plc.AO(0,0)

Returns the current value of the analog output as a Lua number.

Returns a string representation of the analog output with its address and the current state.

Sets the analog output to the passed value, a Lua number.

The value is passed „as is“ to the bus coupler. No conversion takes place.

Initializes the timer. callback is the function to be called when the timer expires.

This Example prepares the timer to print something periodically. Note hat it is necessary to call plc.timer_settime() after plc.timer_init():

plc.timer_init(
   function() print("Timer tick") end
)

Starts (arms) or stops (disarms) the timer. The timer must be initialized at least once with plc.timer_init() before.

secs and usecs is the interval time in seconds and microseconds, just like the struct timeval of C.

Passing 0 s and 0 µs stops the timer.

The Example start the timer, wich expires every 500 ms:

plc.timer_settime(0, 500000)