Horset development was inspired by GRAFCET and  SFC (Sequential Function Chart) part of IEC1131-3 standard. The program combines graphic structure of control process with description of instructions executed at the states and conditions determining transitions of control process from one state to another.

Instructions executed at the state are written immediately to the right and down from the state graphic shape. The transition logic condition is written to the right and down from the transition graphic shape. Any state can have many transitions to different next states. The transition conditions are evaluated from the left to the right till some of them is true. At this moment control process goes to the state subsequent the active transition, executes instructions written at this states and evaluates its conditions. 

Horset allows to create parallel processes. Any control process can create one or more next parallel processes. Two or more control processes can join to one process. The control process can be also killed by other process. The states of active parallel processes are executed step by step. At one program control loop active state instructions and its transition conditions of any active parallel process is executed. The state instructions are executed only once. If no transition condition of the state is true, only transition conditions of the state are evaluated in the next loop. NLC-3 allows minimum one and maximum 16 active parallel processes at one moment.

Inputs, outputs, variables and fields symbolic names are defined at tables. Variables can be defined as boolean, byte, integer and long type. Fields are of integer type. The names of inputs, outputs and variables of other NLC systems connected by CAN and included in project can be used like its own.

At this picture you can see a simple program - the test of 24 NLC-3 inputs and outputs  by using indirect addressing. At the first state index variable i is zeroed. The condition for transition to the next state is always true. At the state 2 at the first line the address of tested input is calculated.  The base address of tested inputs is assigned to in variable at first and the the index variable i is added. The address of switched on output is calculated at the second line of state 2. The base address of tested outputs is assigned to out variable at first and the the index variable i is added. The output with calculated address is switched on by instruction on @out at the third line.

The condition for transition from state 2 to state 3 is true, when the input with indirect address @in is switched on. Index variable i is incremented at the state 3. The state 3 has 2 alternative conditions for transition to the next state. If index variable i is less then 24, program goes to state 2 and tests the next input. If i is equal 24, program goes to state 1 and starts the new test cycle. 

Horset programming system was developed by programmers with wide experience of control systems implementation in different types of technology. We developed and implemented at the end users control systems of robots, monorail transport systems, weighing systems, data acquisition systems, temperature regulation systems, etc.,etc. Thanks to that Horset contains a lot of useful instructions that allows write application software quickly, effectively and the software is well readable and understandable.