> For the complete documentation index, see [llms.txt](https://docs.videc.de/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.videc.de/acron-9.3/en/anlagenkonfiguration/prozessanbindung/provider/providerid/treiberauswahl/dde_dynamic-data-exchange/dde_zyklisch.md).
# DDE cyclic
When using this DDE interface the ACRON Provider polls the values cyclically from the DDE Server and saves them to the ACRON database. Value changes between two polling cycles are not registered. Service data can also be imported. As value changes between two polling cycles are not registered, though, service pulses produce an inaccuracy which increases as the read interval lengthens.
If the value changes from ZERO to a different value, ACRON assumes that the unit has been switched on. If the value changes from not equal to ZERO to ZERO, ACRON assumes that the unit has been switched off.
### Syntax of external variable
DDE variable name; for the exact syntax refer to the description of the DDE server.
## Driver
### Driver file
Display the name of the selected driver and select a driver from the list of installed drivers
### Version
Version of the driver file
### Interface type
Display the driver interface type
### Data transfer type
Description of the data transfer type
## Driver parameters
### Service
See relevant product documentation for DDE Server
### Topic
Program name of DDE Server without extension
## Settings
### Measure interval
This setting indicates the time interval in which values are polled by the control system/PLC. The minimum value depends on the efficiency of the corresponding interface and the number of external variables being logged.
Recommended entry: > 5 sec.
### Polling delay after start
Start of data logging in seconds after the ACRON Provider has successfully established process communication. This is useful, for example, if the opposite party takes some time after a restart to initialize all the variables.
Recommended entry: Depending on the time the DDE server takes to start up, about 10-60 seconds
### Always display provider window on top
Provider windows are always displayed on top
### Activate test mode
Display a window with diagnostic messages
On startup the ACRON Provider opens a window with diagnostic messages. The log file is stored under the relevant provider name in the ACRON installation path, in the `Log` directory.
Note
As diagnosis mode heavily influences the performance of the application, and the recorded messages can normally only be evaluated by Technical Support, you should only activate it when prompted to do so by Support.
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