Device-specific system items

System Item Name (Type)

Type/Access Rights

Description

Values

$SYS$Status

Boolean/Read

Binary status indication of the connection state to the device (hierarchy level) the item is attached to. The device group (OPC access path/topic) does not affect the value.

The status can be good even if individual items have errors.

For DDE/SuiteLink clients, $SYS$Status always comes from the leaf level of a Communication Driver hierarchy branch, which is the destination PLC node. For OPC clients, $SYS$Status can be accessed at all hierarchy levels. $SYS$Status at the root level of the whole hierarchy tree is always good, as it represents the quality status of the local computer itself. Hence, for practical application, OPC clients should reference $SYS$Status at any hierarchy levels other than the root.

RANGE: 0, 1

1: Connection to the device is intact.

0: Error communicating with the device.

$SYS$ErrorCode

Longint/Read

Detailed error code of the communications state to the device.

The device group (OPC access path/topic) does not affect the value.

>= 0: Good status (0 is the default state – connected.

>0: is some device state like: connecting, initializing, etc.

<0: Error status (value indicates the error).

$SYS$ErrorText

String/Read

Detailed error string of the communications state of the device.

The device group (OPC access path/topic) does not affect the value.

Descriptive text for the communications state corresponding to the error code.

$SYS$StoreSettings

Integer/ReadWrite

Makes the temporary update interval changes via the $SYS$UpdateInterval item permanent. If the client pokes a value of 1 into this system item, the currently set update interval is written to the server’s configuration file.

The value of this system item clears to 0 after being set, if the configuration file write is successful. If the write fails, then the value is set to -1.

If the update interval changes via the $SYS$UpdateInterval item and this item is not poked to 1, the Communication Driver uses the original update interval for that topic the next time it is started.

Reading the item always provides 0. Read/Write values are persisted only if you set this system item.

RANGE: -1, 0, 1

-1: Error occurred during saving the configuration file.

0: Read value always if status is OK.

1: Persist settings (cleared immediately).