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Software Configuration
Microsoft Windows Version 3.x.
The Windows environment now supports up to four serial
ports, RS232, RS422 and RS485 etc.
If more than 2 serial ports are installed then the default
assignments assumed by Windows need to be changed. Windows
assumes that both COM1 and COM3 are on IRQ4 and that both
COM2 and COM4 are on IRQ3. Since the PC bus does not allow
interrupt sharing, these pairs of ports cannot be used
simultaneously, seriously limiting the flexibility of Windows 3.1.
To obtain trouble free mix and match of the COM ports,
Set COM3 and COM4 interrupts to ones not used by other
devices on your system, say IRQ10 and IRQ11.
From the Windows Program Manager select Main. Then double
click the Control Panel icon.
From the Control Panel window select Ports.
Chapter 4 Page 36
AT & OPTO DUAL RS422/485
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