While direct port access is possible for some ports, it??™s rarely useful.
Under DOS and early Windows editions, most serial ports used standard port
addresses, and applications could read and write to these addresses using assembly
code or functions, often called Inp and Out.
Under recent operating systems, accessing port addresses requires a low-level
driver such as inpout32 (available from www.Lvr.com). USB virtual COM port
devices don??™t have dedicated port addresses and might not have a UART at all.
Beyond these limitations, using .NET??™s SerialPort class or an equivalent driver
has many benefits. Applications can still access the UART??™s registers, but do so
indirectly and without having to know the port address or other hardware
details. Plus, serial-port classes and drivers offer built-in efficiencies such as
buffering of serial data.
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4
RS-232 is an interface that is suitable for many basic communication tasks
between two computers. This chapter introduces RS-232 signals and interfacing
options.
!
RS-232 is designed to handle communications between two devices with a distance
limit of around 80 to 130 ft, depending on the bit rate and cable type.
RS-232 uses unbalanced, or single-ended, lines. Each signal in the interface has
one dedicated line whose voltage is referenced to a common ground.
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