How to Troubleshoot a Serial Poll Timeout

Serial ports transmit and receive data as sequences of binary data.

Serial polling is a technique used to read input from a computer serial port. Polling checks to see if data has been received by the serial port in an endless loop. If data has been received, it can be read by the program. Since serial polling uses an endless loop, a timer can be used to check and see how long a polling has been active. If enough time has elapsed without any activity, a timeout error can occur, signifying that no data has been received. There are several things you can check to troubleshoot a timeout error.

Things You'll Need

• Computer with serial polling program
• Serial transmission device
• Serial cable

Instructions

1. Examine the serial port cable connections on both the polling computer and the transmitting device.

2. Verify that the serial port connections are attached firmly to the serial port on each device. The connector may have two screws that hold the cable in place. Make sure each screw is firmly screwed into the port.

3. Verify that the device being polled is powered on and transmitting data. If it is powered off or in a mode that prevents data from being transmitted, the device that polls the serial port will not detect any data and timeout.

References

• Beyond Logic: Interfacing the Serial / RS-232 Port
• DEMIC: Serial Polling and SRQ Servicing with NI-488.2 Software and LabVIEW