Avaya 3910 Guide De Branchement
Appendix B: PC Serial Ports
Serial Ports Under Windows 3.1
Unlike the DOS-only world of yesterday, today’s multitasking environments like
Windows permit the microprocessor to communicate with up to four active
serial port devices at the same time (COM1 through COM4). For example,
under Windows, if you are using a serial mouse (on COM1 ) within a terminal
emulator program which operates a data modem (on COM2), while using a fax
serial port devices at the same time (COM1 through COM4). For example,
under Windows, if you are using a serial mouse (on COM1 ) within a terminal
emulator program which operates a data modem (on COM2), while using a fax
board (on COM3) to transmit or receive a fax "in the background," you are
using three serial port devices simultaneously. You might even wish to make a
phone call using PassageWay Solution (on COM4) at the same time, bringing
using three serial port devices simultaneously. You might even wish to make a
phone call using PassageWay Solution (on COM4) at the same time, bringing
the total up to four simultaneously active serial port devices.
The fact that Windows permits this kind of powerful multitasking does not
guarantee that the underlying PC hardware can support this level of operation,
at least without some customizing at the hardware level. Since some PCs can
support it by default (for example, those which support IRQ sharing), Windows
doesn’t prohibit you from configuring your system and attempting tasks like the
one in the previous paragraph. Unfortunately, most PCs cannot support this
operation by default and the most likely result of attempting the above
scenario is "hanging" the PC due to an IRQ conflict. On such systems, using
COM1 along with COM2 is generally fine (recall that these devices have
unique IRQs by default), but the addition of COM3 or COM4 causes the
system to fail.
guarantee that the underlying PC hardware can support this level of operation,
at least without some customizing at the hardware level. Since some PCs can
support it by default (for example, those which support IRQ sharing), Windows
doesn’t prohibit you from configuring your system and attempting tasks like the
one in the previous paragraph. Unfortunately, most PCs cannot support this
operation by default and the most likely result of attempting the above
scenario is "hanging" the PC due to an IRQ conflict. On such systems, using
COM1 along with COM2 is generally fine (recall that these devices have
unique IRQs by default), but the addition of COM3 or COM4 causes the
system to fail.
Fortunately, Windows 3.1 permits complete customization of all parameters
involving serial ports through the Control Panel, including configuring
nonstandard I/O port addresses and IRQs (that is, values different from those
in the table – these parameters can be viewed and/or modified by selecting
involving serial ports through the Control Panel, including configuring
nonstandard I/O port addresses and IRQs (that is, values different from those
in the table – these parameters can be viewed and/or modified by selecting
the desired port in the Control Panel’s "Ports" applet, selecting the "Settings..."
button, then selecting the "Advanced..." button). This flexibility offers the
opportunity of salvation for owners of PCs which do not support IRQ sharing
who require the use of three or more COM ports simultaneously.
opportunity of salvation for owners of PCs which do not support IRQ sharing
who require the use of three or more COM ports simultaneously.
B-6