{"id":881,"date":"2026-03-03T00:07:39","date_gmt":"2026-03-02T22:07:39","guid":{"rendered":"http:\/\/docklight.de\/dl_prb032\/"},"modified":"2026-03-03T00:07:41","modified_gmt":"2026-03-02T22:07:41","slug":"dl_prb032","status":"publish","type":"post","link":"https:\/\/docklight.de\/dl_prb032\/","title":{"rendered":"When trying to open a COM port, I receive an error “Windows error #31 – A device attached to the system is not functioning” or similar"},"content":{"rendered":"

Applies to: Docklight \/ Docklight Scripting (all versions), Article ID: dl_prb032<\/em><\/p>\n

Some serial driver implementations, e.g for USB devices that add a virtual COM port on the PC, do not allow to set the “classic” RS232 communication settings like IOCTL_SERIAL_SET_BAUD_RATE. For many of these applications, the serial data settings are indeed not necessary but the driver accepts them and does not report an error. In case your device driver DOES produce an error and Docklight cannot open the COM port, please use the Project Setting ‘Baud Rate = None’, available in Docklight V2.0 and higher. <\/p>\n

NOTE: A specific example for the above behavior seems to be the Microchip CDC sample implementation. If the following definition is commented out (not defined):
\n‘#define USB_CDC_SUPPORT_ABSTRACT_CONTROL_MANAGEMENT_CAPABILITIES_D1’,
\nthen the device can only be opened with Docklight using the ‘Baud Rate = None’ setting:<\/p>\n

Docklight Downloads<\/a><\/p>\n

<\/a><\/p>\n

<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Applies to: Docklight \/ Docklight Scripting (all versions), Article ID: dl_prb032 Some serial driver implementations, e.g for USB devices that add a virtual COM port on the PC, do not allow to set the “classic” RS232 communication settings like IOCTL_SERIAL_SET_BAUD_RATE. For many of these applications, the serial data settings are indeed not necessary but the driver accepts them and does […]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,8],"tags":[57],"class_list":["post-881","post","type-post","status-publish","format-standard","hentry","category-support","category-troubleshooting","tag-dl_prb032"],"yoast_head":"\nDocklight - When trying to open a COM port, I receive an error "Windows error #31 - A device attached to the system is not functioning" or similar<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/docklight.de\/dl_prb032\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Docklight - When trying to open a COM port, I receive an error "Windows error #31 - A device attached to the system is not functioning" or similar\" \/>\n<meta property=\"og:description\" content=\"Applies to: Docklight \/ Docklight Scripting (all versions), Article ID: dl_prb032 Some serial driver implementations, e.g for USB devices that add a virtual COM port on the PC, do not allow to set the “classic” RS232 communication settings like IOCTL_SERIAL_SET_BAUD_RATE. 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