R_B: Read binary

R_B reads Present value and additional specified properties of a binary data point.

Compatible data points:

Binary input [BI]
Binary output [BO]
Binary calculated value [BCalcVal]
Binary configuration value [BCnfVal]
Binary process value [BPrcVal]
Third party objects which contain the required properties.

Refer to data point objects for a detailed description of the BACnet data points.

Required properties:

Present value
State flag

Optional properties:

Reliability
Update count

Hardware interrupt

This XFB supports hardware interrupts (OB trigger) for immediate response to specific events such as manual switching of lights. If the XFB is applied in a chart assigned to OB40 or OB41, OB triggering occurs automatically on interrupt signals from I/O modules.

Pin description (inputs)

BaObjRef
BA-Object reference Structure [BaObjRef] defines a bound connection between XFB and BACnet object. The binding occurs automatically. Manual configuration attempts are not necessary and can result in system errors.
DeviceId	Device identifier Double word (default value: 16#3FFFFF) [DeviceId] comprises object type and object instance in a single identifier. It is used to identify device object: local or remote. Local device object could also be identified by value 16#3FFFFF.
ObjectId	Object identifier Double word (default value: 16#3FFFFF) [ObjectId] comprises object type and object instance in a single identifier. It is used to identify object within a device.
ItemId	Item identifier Integer (default value: -1) [ItemId] represents an item index in the functional view node object, which references the BACnet object. [ObjectId] and [ItemId] together define an indirect access reference to the BACnet object. Value -1 indicates that direct binding is used.

Pin description (outputs)

PrVal
Present value Boolean (default value: False) The value of the Present value property from the referenced BACnet object. [PrVal] will deliver the last valid value if [Valid] = False.

PrVal

Present value

Boolean (default value: False)

The value of the Present value property from the referenced BACnet object.

[PrVal] will deliver the last valid value if [Valid] = False.

Valid
Valid Boolean (default value: False) An indication of whether output pin [PrVal] is reliable.
1 (True)	[PrVal] is reliable. XFB can access the BACnet object. AND Fault flag in state flag property = 0 (no fault) (Reliability = 0 (no error) or Reliability was not detected).
0 (False)	[PrVal] is not reliable. XFB cannot access the BACnet object. OR Fault flag in state flag property = 1 (fault) (Reliability ≠ 0).

Valid

Boolean (default value: False)

An indication of whether output pin [PrVal] is reliable.

1 (True)

[PrVal] is reliable.

XFB can access the BACnet object.

AND

Fault flag in state flag property = 0 (no fault)
(Reliability = 0 (no error) or Reliability was not detected).

0 (False)

[PrVal] is not reliable.

XFB cannot access the BACnet object.

Fault flag in state flag property = 1 (fault)
(Reliability ≠ 0).

UpdInd
Update indication Boolean (default value: False) An indication of whether the Present value property has been newly updated. When an update occurs, [UpdInd] toggles from 0 to 1 (True) and returns to 0 (False) on the next cycle (immediate). It is not possible to detect the toggle without an additional function block connected to [UpdInd] (for example, a counter function block). [UpdInd] will only be set to True if [Valid] is True. [UpdInd] uses the update count property if present. This makes it possible to recognize a value as having been updated in cases where the new value is the same as the previous value. For objects without update count, [UpdInd] toggles on a change to Present value.

UpdInd

Update indication

Boolean (default value: False)

An indication of whether the Present value property has been newly updated.

When an update occurs, [UpdInd] toggles from 0 to 1 (True) and returns to 0 (False) on the next cycle (immediate). It is not possible to detect the toggle without an additional function block connected to [UpdInd] (for example, a counter function block). [UpdInd] will only be set to True if [Valid] is True.

[UpdInd] uses the update count property if present. This makes it possible to recognize a value as having been updated in cases where the new value is the same as the previous value. For objects without update count, [UpdInd] toggles on a change to Present value.

ErrCode
Error code indication Integer (default value: 20) The status of the last performance of the XFB read operation.
= 0	No error.
> 0	Error, see XFB error codes.

ErrCode

Error code indication

Integer (default value: 20)

The status of the last performance of the XFB read operation.

= 0

No error.

> 0

Error, see XFB error codes.

Use case examples

NOTICE

Note
Graphics reflect examples of XFB implementations; See ABT for current examples of CFC.

Simple use: the present value is used without checking the Valid pin.

Standard use: the present value is used only if Valid is True.