Device group-specific system items

$SYS$UpdateInterval

Not used.

$SYS$MaxInterval

Not used.

$SYS$WriteComplete

Integer/

ReadWrite

Accesses the state of pending write activities on the corresponding device group. On device group creation (adding items to an OPC group), the value of this system item is initially 1

If the value is not zero, the client can poke 1 or -1 to it (poke a 1 to clear errors, or a -1 to test a client reaction on write errors). If the value of this item is zero, it cannot be poked.

RANGE: -1, 0, 1

1: Write complete (no writes are pending – initial state).

0: Writes are pending.

-1: Writes completed with errors.

$SYS$ReadComplete

Integer/ ReadWrite

Accesses the state of initial reads on all items in the corresponding device group.

Poking a 0 resets the internal read states of all items in this device group. This resets this item to 0. If all items are read again after this poke, this item changes back to 1 or -1.

RANGE: -1, 0, 1

1: Read complete (all values have been read).

0: Not all values have been read.

-1: All values have been read but some have a non-good quality.

$SYS$ItemCount

DWord/

Read

Accesses the number of items in the corresponding device group. This item is read-only.

RANGE: 0…2147483647

>=0: Number of active items.

$SYS$ActiveItemCount

DWord/

Read

Accesses the number of active items in the corresponding device group. This item is read-only.

RANGE: 0…2147483647

>=0: Number of active items.

$SYS$ErrorCount

DWord/

Read

Accesses the number of all items (active and inactive) that have errors (non-good OPC quality) in the corresponding topic.

If the communications status of a device group is bad, all items have errors. This item is read-only.

RANGE: 0…2147483647

>=0: Number of all items (active and inactive) with errors.

$SYS$PollNow

Boolean/

ReadWrite

Poking a 1 to this item forces all items in the corresponding device group to be read immediately.

This is useful if you want to force to get the newest values from the device, regardless of its update interval.

This also works on device groups with a zero update interval (manual protocol triggering).

RANGE: 0, 1,