The card is plugged in, but the COM port cannot be seen in the device manager. This is the most frequent problem in serial port card after-sales consultation. In most cases, there is no need to change the card. If you check in the following order, the cause can usually be located within 20 minutes.

Step 1: Confirm whether the system really recognizes the card

First check if there are any unknown devices or PCI simple communication devices with an exclamation mark in the device manager: if there are, the driver is probably missing or incorrectly signed. If there is no change at all, check whether the card is inserted in place and whether the slot is powered. You can try another PCIe slot and try again. oldPCI serial cardWhen installing on a new motherboard, also pay attention to the CSM and Legacy related switches in the BIOS.

Step 2: Handle COM number conflicts

• The onboard serial port occupies COM1 and COM2. The card ports are arranged from high to high. Change the software fixed ports to the same number segment;
• After changing the port number, restart the collection software to avoid caching of old handles;
• If multiple software competes for the same COM, shut down redundant processes first and then test separately.

Step 3: The port is connected but data is still lost, check the parameters and direction.

The baud rate, data bits, and parity bits must be exactly the same as those on the device;PCI-E to 4-port RS485/422 serial port cardWhen running 485, you must also confirm the half-duplex direction switching setting, otherwise it will be sent but not received. Change the short wire or shielded twisted pair and test again to quickly verify whether it is line interference.

Locate according to the four segments of identification, number source, parameters, and line. Most port problems can be solved by yourself. If you still can't find the problem, you can call EB-LINK technical support at 0755-83179002, and an engineer will remotely view the logs.