## 1 Introduction  
Displacement control of linear or rotary hydraulic drives is based on the use of variable displacement pumps [1]. This type of control is justified in being used for capacities above \(2\div 4\) kW, or depending on the specific requirements for the hydraulic drive system. Often, the pumps used in such systems are an axial piston type [2]. This is a consequence of a number of their advantages over other types of hydraulic displacement rotary machines. These advantages are summarized in the following: a high density of transmitted power per unit of weight; the possibility of operation at high pressures (approximately 45 MPa); operation at high rotation frequencies (approximately 450 rpm); compact overall dimensions; operation in closed and open circuits; and the implementation of various control laws of flow rate, pressure, and power. The last two advantages are the main reason for the use of axial piston pumps, both in industrial and mobile applications [3]. The research and development of these pumps is in two main directions. The first is the development of the construction [4, 5, 6, 7] of the piston (rotary) group in order to increase their efficiency [8], and the second is related to the improvement in the regulating devices and the ways of displacement volume control [9, 10, 11, 12]. The second direction further increases the area of their application, as it stimulates the development of hydraulic drives, allowing higher values of the overall efficiency. Along with efficiency, the improvement in regulating devices also requires higher control performance [13]. As is known with displacement control, the transition time (when changing to different operating modes) is greater than throttle control. In retrospect, this is also the main reason for the introduction of proportional electro-hydraulic control devices to replace the classic hydro-mechanical controllers. Thisfact accelerates the development of another direction based on variable displacement hydraulic pumps and hydraulic motors (most often of the axial piston type) named for short as \"secondary control\" [14; 15]. Abstracting from the wide field of application, both in open and closed circulation, the introduction of installation-specific proportional valves in the control of axial piston pumps largely overcomes the limitations in transitions in different operating modes. In most cases, however, the control is limited by the selective electronic amplifiers designed for the valve, which are an analog circuit implementing a classic PID control law [16; 17; 18]. The development of digital signal processors allows the realization of advanced control laws in programmable platforms, which is the basis of modern control systems called embedded control [19]. These laws most often use an algorithm in which performance criteria are used on the transfer matrix of the plant. By applying it to the control of a variable displacement axial piston pump, the control performance is significantly improved [20; 21; 22; 23; 24], and without the use of a special selective electronic amplifier, but only by the use of PLC. These facts briefly describing the current state of the affairs motivates the authors to develop rapid prototyping of real-time control algorithms for open-circuit variable displacement axial piston pumps. In the present article, the system for the rapid prototyping of real-time control algorithms for open-circuit variable displacement axial piston pumps is presented. The developed solution suggests using an embedded approach for the prototyping of various algorithms. For the aim of axial piston pump real-time control, the custom CAN communication protocol operating on 10 ms is developed. It is also used for communication and synchronization with the embedded programmable logic controller of an axial piston pump. Moreover, this protocol is realized as a new Simulink(r) S-function, which is a part of the proposed main Simulink(r) model.