Multiple COM ports under Windows NT (sharing the same IRQ)

---

Multiple COM ports under Windows NT (sharing the same IRQ):

A good multiple serial port interface card is Advantech PC-LabCard PCL-746+ which has 4 COM ports which indivdually can be set to either RS232, RS422 or RS485. The card uses the standard UART 16C550, which has an onboard 16 byte FIFO. The address of the card has a lot of possiblities and the IRQ likewise (there is though only one IRQ per card, ie it is shared among the 4 ports). The card will be used for the communication with the undulator for ASTRID and for the monocromator for the undulator. The card has been bought from DanBit (order nr 4SER+UNI) at a price of app. 1500 kr.

SETUP: In Control Panel is the COM-port icon selected and the four COM-ports are added, with the choosen cardsettings for the address and the IRQ. (These of cause has to be choosen not to conflict with other hardware in the machine - use for instance the Windows NT diagnostic program, and select IRQ/Port status to check present hardware).  The card should be used in enhanced mode. To enable the sharing of the same IRQ line the registry unfornately has to be edited by hand. Open the registry editor (regedt32) and in the key HKEY_Local_Machine/SYSTEM/CurrentControlSet/Services/Serial the PermitShare has to be changed from x0h to x1h.

Addendum:
Advantech now has a new revision (Rev. B1) where each port can be setup indivdual. If this option is not choosen the above can still be used.

 

 

---

Last Modified 11 January 2019