Additional Global Parameters
The following global variables will supersede default values and the values defined in the .ini file unless otherwise noted:
Writing Single Coils
Some devices use the Force Single Coil command (function code 5) for writing single coils.
Other devices support (sometimes exclusively) the Force Multiple Coils (function code 15) when writing coils.
You can configure the Modbus Ethernet communication interface to use a specific function code when writing single coils and when interacting with a particular device.
DeviceId_
ONE_COIL_WRITE
| For | Project | |
| Purpose | To control the behavior, for writing single coils on a specific device | |
| Value | Y | Will cause function code 5 to be used. |
| N | Will cause function code 15 to be used. | |
| Comment | For device models Modicon 484, VersaMax ENIU and VersaPoint ENIUs, single coils writes will be selected regardless of the user-configured preferences. | |
Writing Single Holding Registers
Some devices use the Force Single Holding Registers command (function code 6) to write a single holding register.
Other devices support (sometimes exclusively) the Force Multiple Holding Registers Command (Function Code 16).
DeviceId_
ONE_REG_WRITE
| For | Project | |
| Purpose | To control the behavior, for writing single holding registers on a specific device | |
| Value | Y | Will cause function code 6 to be used. |
| N | Will cause function code 16 to be used. | |
| Comment | For device models Modicon 484, VersaMax ENIU and VersaPoint ENIUs, when performing a request to write a single register, single register writes will be selected regardless of the user configured preferences. | |
Connection Conservation
Some devices will terminate a connection if there is no activity for some pre-configured interval.
DeviceId
_CONSERVES_CONN
| For | Project | |
| Purpose: | To re-define how the device communication interface handles a disconnect as it relates to device down for some devices that terminate a connection if there is no activity for some pre-configured interval. | |
| Value: | Y | The device will not be declared down unless it is unable to re-establish the connection and perform the next immediate I/O operation to request or modify data on the device. |
| Comment | For device model VersaPoint ENIU, the device communication interface will perform specific processing that overrides the behavior of this setting. | |
Host Redundancy with Devices with One Connection
Some devices will support only one connection.
In host redundant environments, it is necessary to identify the devices with this characteristic so that the connection can be terminated on the acting secondary and initiated on the primary following a transition in the host redundancy roles.
Note that a device down will not be generated as a result of not having a connection with the secondary. To identify a device that supports only a single connection, define the following project level global parameter.
DeviceId_CONN_SECONDARY
| For | Project | |
| Purpose | To identify a device that supports only a single connection. | |
| Value | N | |