Networking Devices Objectives

Table 3.2
Common Serial (COM) Port Resource Assignments
Port ID
IRQ
I/O Address
Associated Serial I/F Number
COM1
4
03F8
1
COM2
3
02F8
2
COM3
4
03E8
1
COM4
3
02E8
2
For external modems, you need not concern yourself directly with these port
assignments, as the modem connects to the serial port and uses the resources
assigned to it. This is a much more straightforward approach and one
favored by those who work with modems on a regular basis. For PCMCIA
and USB modems, the plug-and-play nature of these devices makes them
simple to configure, and no manual resource assignment is required. Once
the modem is installed and recognized by the system, drivers must be con-
figured to enable use of the device.
Two factors directly affect the speed of the modem connection—the speed of
the modem itself and the speed of the Universal Asynchronous
Receiver/Transmitter (UART) chip in the computer that is connected to the
modem. The UART chip controls the serial communication of a computer,
and although modern systems have UART chips that can accommodate far
greater speeds than the modem is capable of, older systems should be
checked to make sure that the UART chip is of sufficient speed to support
the modem speed. The UART chip installed in the system can normally be
determined by looking at the documentation that comes with the system.
Table 3.3 shows the maximum speed of the commonly used UART chip
types.
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Chapter 3
74
Table 3.3
UART Chip Speeds