Page 527 - Sensors and Control Systems in Manufacturing

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Cha p te r
Ni ne

FIGURE 9.39 Several devices communicating with one another using parallel
transmission, with precise coordination of data fl ow.

If several devices are to communicate with one another according
to the principle of parallel transmission, precise coordination of the
data flow is necessary (Fig. 9.39).
The devices are divided into four groups:
• Talkers: able only to transmit, such as sensors
• Listeners: able only to receive, such as printers
• Talkers/listeners: can transmit and receive, such as floppy
disks
• Controllers: can coordinate data exchange, such as computers

Each device is allocated a specific address. The controller decides
between which two devices data exchange is to be carried out. Two
standards describe the technique of transmitting interface functions:
standards IEC-625 and IEEE-488. The number of data and control lines
is specified in the standards as eight each. Up to 30 devices can be con-
nected to the bus; the complete system of lines may not be longer than
20 m. Maximum transmission speed is between 250 and 500 kb/s.
In general, it can be said that relatively fast data transmission,
such as several hundred thousand characters per second, can be
achieved with parallel interfaces. However, transmission length is
limited to several meters.

9.12 Serial Data Transmission
Figure 9.40 illustrates the principle of serial data transmission. Only
one line is available for serial data transmission. This means that an