Below are the hardware and software conditions that I encountered during my project: a laptop without an RS232 serial port, an OMRON CPM2AH-60 CDR type PLC, and the Cx-Programmer V5.0 programming software. 1. Communication between Cx-Programmer V5.0 and the PLC is unstable: The connection path was as follows: Laptop USB port (no RS232 port) → [USB to RS232 cable (with driver installed, default COM4 set to COM1)] → [RS232 male] → [PLC RS232 female]. The cables were connected through a series of adapters. There were two types of cables used. The first one followed the official Omron wiring (2-2, 3-3, 9-9 shorted), while the second one used a conventional RS232 setup (2-2, 3-3, 5-5 shorted). Through testing, both could work, but the first type provided more stable communication. The second type had issues with frame loss when communicating via VC applications, which could be resolved by ensuring a shared ground between the computer and PLC. At times, the communication would fail with the error message: "Modem has been selected, continue code?" (which should actually be "continue?"). This issue could be fixed by deactivating the modem in the Device Manager. It's also important to ensure that the correct COM port (like COM1) is being used, and that the USB ports are properly matched. A few times, even after reinstalling the OS or re-installing the software, the issue would return unless the program was carefully backed up and rebuilt from scratch. 2. Communication interference with Cx-Programmer V5.0: When the system was under load—such as when 20 AC contactors were turned off simultaneously—the PLC would lose communication. However, this only happened during shutdown, not during startup. One possible solution is to reconnect the PLC after such events. For a more permanent fix, adding RC modules to each contactor coil might help, though this hasn't been tested personally. 3. Testing direct USB-to-RS232 connection: I tried connecting the PLC directly via a USB-to-RS232 cable instead of using a dedicated connection cable. But this led to errors like "The selected port is occupied by another application." After analysis, it was suspected that the direct connection might cause improper pin mapping (e.g., 2-2, 3-3, 5-5 shorted, but others not), potentially leading to communication issues or even damage to the ports. It’s safer to use the proper connection cable that matches the official wiring scheme. HP Laptop 15-FC 15-FD,HP laptop 15-FC keyboard,HP laptop 15-FD keyboard,HP 15-FC back cover S-yuan Electronic Technology Limited , https://www.syuanelectronic.com