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1. PLC/terminal communications dialog principle
The communications dialog between the terminal and the PLC consists of an exchange of data between one or several devices.
In all communication situations, the following should be defined:
- Data to be exchanged,
- Communication protocol.
Data exchanged
Various types of data can be exchanged.
PLC
Data associated with fields
Command data sent from the PLC to the terminal
TERMINAL
Status data sent fron the terminal to the PLC
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Graphic Magelis
1. PLC/terminal communications dialog principle
Data associated with fields
These are variables which may be:
- displayed on the terminal,
- entered or modified on the terminal.
Command data sent by the PLC to the terminal
This concerns the following commands:
- Display an application or system page,
- Display an alarm page,
- Lock keys,
- Request to enter a variable field,
- Print command,
- Command of indicator lights associated with function keys,
- Clear log command,
- Set time-stamp command,
- Triggers graph plotting.
- etc.
Status data sent by the terminal to the PLC
This concerns the following status:
- Terminal status
- confidential mode,
- terminal configuration mode,
- confirmation of entries by pressing the ENTER key,
- cancelled entry by pressing the ESC key,
- cancelled entry after a time-out,
- print fault.
- Number of the displayed page,
- Number of the last field entered,
- Image of the keypad keys,
- Time-stamp status (date and time),
- Log occupancy rate as a percentage,
- Communication monitoring,
- Number of the last alarm acknowledged,
- Application signature,
- etc.
Graphic Magelis
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