The AT COM Board manual numbers the COM ports from 5 to 8. The ori-
gin of this numbering is from the BEETLE, which has COM1 to COM4 on
the motherboard. It is recommended for consistency, that you use this
numbering also, regardless whether you have e.g. a BEETLE (with COM
ports 1,...,4) or a PC (with e.g. only COM1 and 2).
To provide for a numbering according to that, the following procedure is re-
commendable:
1. run the Add New Hardware wizard to configure new COM ports, so ad-
ding possibly COM3, COM4, if not already present and COM5, COM6 and
(if you have) COM7 and COM8
2. delete COM ports, that are physically not available (i.e. served as a pla-
ceholder)
4. reboot to activate the configuration
Using shared interrupts for COM ports with Windows NT
Sharing an interrupt for a COM port under Windows NT requires a specific
configuration in the Registry. To provide for interrupt sharing the steps are:
- run REGEDT32.EXE, which can be called by clicking on Run in the File
menu of the Program Manager
- assure that you have permission to change the Registry, which maybe
only an Administrator is allowed to do
- in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Seri-
al set the value of the variable ‘PermitShare’ to 1
- be careful to do this correctly, since the documentation says that bad Re-
gistry entries may have the result that Windows NT cannot come up; a
good idea could be to backup the Registry before.
Since the ‘PermitShare’ variable has global effect on all COM ports, it is
your responsibility to ensure that sharing of interrupts can be performed
on all COM ports installed. In a PC configuration with COM1 and COM2 in-
tegrated in the motherboard chipset using IRQ4 and IRQ3 rsp., you could
e. g. have the idea to install another ISA multiport card with two ports
COM3 and COM4 and wish to run them with IRQ4 and IRQ3 too. This will
COM Board
GB - 15
