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Automating Manufacturing Systems - Process Control and ...

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plc serial - 27.13<br />

A<br />

ACB<br />

Channel 1<br />

<strong>Control</strong> R6:0<br />

ABL<br />

Channel 1<br />

<strong>Control</strong> R6:1<br />

B<br />

AEX<br />

Source ST9:0<br />

Index 5<br />

Length 2<br />

Dest ST9:1<br />

ASR<br />

StringA ST9:2<br />

StringB ST9:3<br />

O:001/2<br />

Figure 27.11<br />

String Manipulation Functions<br />

The AHL function can be used to do h<strong>and</strong>shaking with a remote serial device.<br />

27.3 PARALLEL COMMUNICATIONS<br />

Parallel data transmission will transmit multiple bits at the same time over multiple<br />

wires. This does allow faster data transmission rates, but the connectors <strong>and</strong> cables<br />

become much larger, more expensive <strong>and</strong> less flexible. These interfaces still use h<strong>and</strong>shaking<br />

to control data flow.<br />

These interfaces are common for computer printer cables <strong>and</strong> short interface<br />

cables, but they are uncommon on PLCs. A list of common interfaces follows.<br />

Centronics printer interface - These are the common printer interface used on most<br />

personal computers. It was made popular by the now defunct Centronics printer<br />

company.<br />

GPIB/IEEE-488 - (General Purpose Instruments Bus) This bus was developed by<br />

Hewlett Packard Inc. for connecting instruments. It is still available as an option

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