Using sha red in ter rupts for COM ports with
Wind ows 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:
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As su re that you have per mis si on to chan ge the Re gi stry
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Run RE GE DIT.EXE or RE GEDT32.EXE
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In HKEY_LO CAL_MA CHI NE\SYS TEM\Cur rent Con trol Set\Ser vi ces\
Se ri al set the value of the variable ‘PermitShare’ to 1. Add this variable in
case it does not exist (DWORD type).
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
integrated 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 be
impossible by hardware reasons! The problem is, that in such a case on the
AT bus two different hardware instances would be “fighting” for the same
IRQ!
Refer to the technical information about your system for the details you
need!
If you configure COM ports to share a common interrupt and ‘Permit Share’
is not set to 1, you could use all COM ports but only one at a time.
use of COM ports like
(only one at a time) not like (parallel)
- open COM n
- use COM n
- close COM
- open COM n+1
- use COM n+1
- close COM n+1
- open COM n
- open COM n
- use COM n
- use COM n+1
- close COM n
- close COM n+1
Check your hardware configuration before using shared COM interrupts!
AD DING COM PORTS
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