Abstract: With the development of touchscreen technology and the improvement of human-machine interface (HMI) functions in production processes, the application of multi-screen HMIs is becoming increasingly common. This article uses clear diagrams and practical engineering development cases to explain in detail how Delta's DOP series achieves multi-screen functionality. Keywords: Human-machine interface, macro instructions 1 Introduction Many HMIs on the market now offer the convenient function of connecting two or more HMIs to one controller, which is commonly referred to as a multi-screen system in engineering. Examples include the WeinView series from Taiwan's Weintech Technology Co., Ltd., and HITEC (Taiwan). Delta's DOP series touchscreens have strong HMI functions, but the Screen Editor software does not provide integrated multi-screen application functionality. This article proposes a multi-screen integration design technology for the DOP touchscreen. 2 Principle Design One of the features of Delta's DOP series touchscreens is that they provide two communication ports, which can be used independently. One communication port can be used to connect to the controller, and the other can be used to connect to a second or third touchscreen. The following will present a multi-screen system design for the DOP series touchscreens using engineering cases. All data exchange between the slave devices and the PLC is completed through macros in the master device. Each HMI can run different programs. By extension, a variation of this approach allows for easy data exchange between multiple HMIs and multiple controllers. 2.1 One-Machine Dual-Screen System Design Figure 1: Block Diagram of a DOP Touchscreen One-Machine Multi-Screen System. Referring to Figure 1, one DOP touchscreen acts as the Master HMI, and several other HMIs act as Slave HMIs, designated as #2, #3, etc. The Master HMI's COM1 is connected to the Delta EH series PLC via RS232, and the Master HMI's COM2 is connected to each Slave HMI via RS485. Thus, the Master HMI acts as the master station on both lines, responsible for exchanging data on both lines. This example uses two HMIs connected to the same PLC. The simplified system diagram in Figure 1 is shown in Figure 2. The two DOP touchscreens are directly connected via MODBUS ASCII. Figure 2. Block Diagram of a DOP Touchscreen Dual-Screen System 2.2 Synchronous Data Display on Both Screens Function 1: Two HMIs simultaneously display PLC data changes. A key feature of DOP is its support for macro instructions, so these functions rely on macros. Let's assume the register addresses used by the PLC in Function 1 are D200 and D201. The corresponding addresses for the Slave HMI are $109 and $110. According to Table 1, the correspondence between DOP internals and MODBUS addresses is W40110 and W40111. Then, in the Master HMI, the BMOV instruction is used to transfer data from area D to area $. Table 1. Correspondence between DOP internal and MODBUS Modbus address HMI internal data definition W40001 ～ W41024 $0 ～ $1023 Internal buffer W42001 ～ W43024 $M0 ～ $M1023 Power-off retention internal buffer W44001 RCPNO Recipe number buffer W45001 ～ ... RCP0 ～ RCPn Recipe buffer B00001 ～ B01024 $2000.0 ～ $2063.15 Internal buffer (bit) B01025 ～ B02048 $M200.0 ～ $M263.15 Power-off retention internal buffer (bit) 2.3 Dual-screen data synchronous modification Function 2: When any one HMI modifies the value of the PLC register, the change can be simultaneously reflected on the other HMI. Referring to Figure 3, to achieve synchronized screen switching between master and slave HMIs, the [System Control Area] is needed. Assume the master and slave HMIs share the slave's MODBUS address W40100 for screen switching. 2.4 Synchronized Screen Switching Between Two HMIs Function 3: When one HMI switches screens, the other HMI will automatically switch as well. Refer to Figure 4, where green indicates execution in Slave HMI #2; orange indicates execution in Master HMI #1. The key to this function is that both the master and slave can modify the data in the PLC. Let the register addresses in the PLC be D100 and D101. The corresponding addresses for Slave HMI #2 are W40010 and W40011. Our approach is as follows: when Master HMI #1 completes the input of values ​​to D100 and D101, a flag bit 1#$101.0 is triggered (1# represents Master HMI #1, 2# represents Slave HMI #2). In macro #1 (background), check if $101 is 1. If so, call submacro #2. In submacro #2, use the BMOV instruction to split D100 and D101 and send them to submacro #2 (W40010 and W40011) to achieve simultaneous data changes. Simultaneously, start the execution macros for D100 and D101, perform a 200ms delay, and then reset $101.0. Following the same procedure, when submacro #2 completes the input of values ​​to submacro #2 (W40010 and W40011), trigger the flag #2 (B00001). Because the address of BasePort or Link2 cannot be directly used in the IF statement of macro #1, it is necessary to first get $100.0 to 2#B00001. Then, in macro #1, check if $100 is 1, and if so, call submacro #1. In submacro #1, use the BMOV instruction to send 2#W40010 and 2#W40011 to D100 and D101 respectively to achieve simultaneous data change. Simultaneously, the macros following the execution of 2#W40010 and 2#W40011 are started, with a 200ms delay, and then 2#B00001 is reset. The diagrams illustrating the three functions are shown below: Figure 3: Dual-screen data synchronization display; Figure 4: Dual-screen data synchronization modification; Figure 5: Dual-screen screen synchronization switching. 3. Screen Editor Software Design The system principle design is implemented using a Screen Editor. Due to space limitations, some basic software operations are not described here; this article only mentions some key points. 3.1 Programming of #1 Master HMI Start the Screen Editor software, create a new file, and set the module parameters. In the diagram above, connect COM1 of #1 Master HMI to the DVP PLC as the PLC's master station. Set the communication parameters with the PLC. Create a new Link2 and use COM2 of #1 Master HMI to connect to #2 Slave HMI, as shown in the diagram. Create a new 1-Screen_1 screen. The attribute settings for D101 are the same as for D100. Create a 2-Screen_1 screen to facilitate screen switching. Create a Background macro for the 2-Screen_2 screen. Create two sub-macros: Sub-macro 1 and Sub-macro 2. At this point, the program for #1 Master HMI is complete. 3.2 Programming of #2 Slave HMI [Setting Module Parameters] Create two screens for #2. At this point, the program for #2 Slave HMI is complete. The actual operation of a dual-screen system is shown in Figure 6. Figure 6. Actual Operation of One Machine with Dual Screens 4. Conclusion Delta Electronics, as an internationally renowned supplier of electromechanical products, produces masterpieces of craftsmanship in every product. The two communication ports of Delta's HMI, used independently and combined with convenient macro instructions, can accomplish many complex communication functions. It is hoped that this example will encourage everyone to explore more potential applications.