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Serial connections

 

Relatively few IT managers get involved with the connection of devices to the computer system, but it might be worth while noting some of the trends.

Remote devices are always serially connected, either directly to digital services or, via modems, to the older analogue systems. Some high performance sub-systems such as storage networks, are connected by specialised high speed networks, but the common local connection is to an Ethernet. There are a number of physical variants on the Ethernet cabling, and there are now two common data rates, !0 or 100 Mbps (note that a low case b means "bit", while an upper case B means "Byte"; there is a lot of confusion created by careless use of abbreviations). A giga bit per second Ethernet is now maturing for backbones and some high speed devices.
Historically most devices such as terminals and printers were serially connected. PCs had two integral serial (COM) ports to support such devices, but in many situations a large number of serial devices had to be connected and so multi-port communication controllers became common. In the corporate world these were dominated by specific systems such as IBM 3745, etc. on mainframes, but minis and the bigger PCs, admittedly with far less capacity, used plug-in interrupt driven controllers.
The bigger Unix machines were among the first to feature the Ethernet as standard, and so years ago they introduced a version of the serial controllers which was attached to the Internet. Standard Unix software exploited the TCP/IP protocol, with higher layer protocols such as telnet, to map characters across the Ethernet to the individual serial ports. The same concept of an Ethernet connected serial communications controller is now common with PCs. Since they are TCP/IP based these controllers can also be sited remotely, across the Internet for example, although the data rates will be lower.
With the new breed of "plug-and-play" PC hardware, the trend is to eliminate the integral serial port. They are also eliminating the internal bus, although PCI will be difficult to eliminate. Directly attached peripherals should thus be attached via USB or Firewire ports. Thus while multi-port internal PCI boards are still common on PCs, the Ethernet attached variety is also now common. With Unix, which is multi-user, there can be mixtures of interactive terminals and data input/output devices to support. With NT, which is single-user, only input/output devices need be supported. This is done via a standard programming API referred to as COMM. Since the data capture and control applications are written to this API, then NT drivers are needed which make PCI bus attached ports and those on Ethernet connected controllers transparent.
Since new PCs and other similar systems now have an integral Ethernet port they no longer are serially connected locally, but they are remotely. The advent of the Internet created a big demand for multi-port serial controllers, with modem support, although recent advances in digital services are seeing Ethernet bridging becoming the alternative for serious users; many hotels have such Ethernet compatible ports in the rooms today. But for some time to come there will be a lot of mobile and home workers who will need to be connected via the old telephone networks, further complicating the issue because a mixture of digital and modem services will inevitably cause incompatibility problems.
For interactive workers the serial connection is becoming less important, but not for other applications. There is still a lot of application software written to send data and commands to devices, as well as to read data, which cannot be trivially altered. Further there is a lot of hardware for process control, factory automation, security systems, EPOS, data logging, and so on, which uses serial connection. In many cases this is because of difficult physical situations. Thus while the need for serially connected PCs and terminals is diminishing, it is still a major requirement for any system which requires data capture and control of other sub-systems.
In practice few IT professionals will need to get directly involved with serial communication products. But "integration" is one of the key buzz words of today, and so it is possible that more IT systems will need to be inter-working with factory systems, security devices, etc. There are of course specialist system integrators who will implement the control and data capture subsystems. They will normally be experienced in interconnection with data processing systems as well. Nevertheless it is wise to be aware of the current trends when dealing with sub- contracted system houses.

Dit artikel is afkomstig van Computable.nl (https://www.computable.nl/artikel/1324785). © Jaarbeurs IT Media.

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