Serial Adapters

Serial adapters provide one or more serial ports to a host computer. They interface with the host computer via a data bus and add RS232, RS422, RS485 and/or other types of serial ports. RS232 is a serial communication standard that provides asynchronous communication capabilities with hardware flow control, software flow control, and parity checking. Most gears, instruments, and digital communication devices are equipped with an RS232 interface. The typical transmission speed for RS232 is 9600 bps at 15 m. RS422 is a serial communication protocol that supports multi-point connections and provides longer transmission distances than RS232. The maximum transmission distance for RS422 is 1.2 km at 110 kbps. RS485 is similar to the RS232 standard, but is actually an enhanced version of RS422. Typically, RS485 is used in applications that require the use of a single controller with multiple devices. Other protocols for serial adapters include inter-integrated circuit (I²C), serial peripheral interface (SPI), and Microwire^® , a registered trademark of National Semiconductor Corporation.

Selecting serial adapters requires an analysis of computer buses and communication standards. Some suppliers provide products that are designed for the general-purpose interface bus (GPIB), universal serial bus (USB), FOUNDATION fieldbus, controller area network bus (CANbus), control network (ControlNet), device network (DeviceNet), attached resource computer network (ARCNET), or process fieldbus (PROFIBUS^® ). PROFIBUS is a registered trademark of PROFIBUS International. Other suppliers provide serial adapters that are designed for technologies such as peripheral component interconnect (PCI), Compact PCI (cPCI), PCI extensions for instrumentation (PXI), PC/104, small computer systems interface (SCSI), VersaModule Eurocard bus (VMEbus) and VME extensions for Instrumentation (VXI). Network protocols for serial adapters include 10Base-T, 10Base-2, 100Base-T, 10/00Base-T, Gigabit Ethernet, Fibre Channel, and IEEE 1394 or FireWire^®, a registered trademark of Apple Computer, Inc. 

Performance specifications for serial adapters include form factor, mounting style, data rate, number of ports, buffer size, and connector type. Some serial communication adapters have a printed circuit board (PCBs) form factor. These devices are designed to attach to enclosures or plug directly into computer backplanes. Other serial adapters mount on racks, shelves, panels, or DIN rails. Desktop and portable serial adapters are also available. For rapid data processing, most products use 16-byte, 32-byte, 64-byte, or 128-byte first in, first out (FIFO) buffers. There are several common connector types, including DB9, DB25, RJ-11, and RJ-45. Bayonet Neil-Concelman (BNC) connectors were designed for military applications, but are used widely in video and RF applications to 2 GHz. BNC connectors have a slotted outer conductor and a plastic dielectric that causes increasing losses at higher frequencies.

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Part Numbers for Serial Adapters