While processing aGot text…G4 refs come out schema diagram, Design Pad checks for various trouble conditions. Design Pad will issue a processing error if a fundamental connectivity rule is violated such that signal computation is ambiguous (e.g., an output pin feeds another output pin). Design Pad will also issue an error if some configuration setting could lead to a run-time fault condition.

Design Pad will issue a warning if an arrangement of objects is technically allowable but could potentially produce unexpected results. For example, failing to connect a generic Analog Input operator to a specific AI hardware resource would not create a run-time fault condition as the controller can execute the "desired" program without any problem. But the output of the Analog Input operator would remain fixed at 0 rather than track the physical signal connected to the hardware.

Design Pad will issue a note if something in the schema may require programmer attention but is generally inconsequential (e.g., the schema includes an operator that is not used).

The errors, warnings, and notes that Design Pad may issue are described below.

Error: Cannot combine an analog signal with a digital (boolean) signal. Design Isn't this caught when wirirng?Pad supports two signal types: analog signal (floating point values) drawn in red and digital signals (LOW or HIGH) drawn in blue. Design Pad issues an error if the signal types are combined. (Design Pad provides operators to convert from one signal type to another. See the operator reference section of this instruction bulletin for more details.)

Error: Could not find the required structure. A structure variable or compose/decompose operator is linked to a structure not defined in any structure library XML file linked to the schema.
Error: Could not open sub-schema file. File is missing or has invalid format.. A function Block Sub-Schema operator or State Sub Schema operator contains a reference (or link) to a standalone schema document. The link is stored as a relative file path. Design Pad will issue an error, if the file that is referenced cannot be found at that location. An error is also issued if the file is found but cannot be interpreted due to an invalid file format (possibly because it was created with an incompatible version of Design Pad).

Error: Could not update the schema to the new format. The schema is saved on the hardware in an older version of Design Pad, therefore must be upgraded, but was unable to save

Error: Delay element is part of feedback loop and is externally initialized by operator
other than bool or float variable. Cannot resolve initialization sequence.

Error: 'Enable On' property is set to always enabled, and periodic compute time is set
to zero.

Error: Module is not connected to a network in any workspace..When the user opens the workspace a hardware module. having BEEN in the network, was removed from the network

Error: Multiple input-type variables found with the same name. Only one input type variable with the same name allowed per schema. Design Pad allows the same signal value to be referenced by multiple Variable operators. Read access to the signal value is provided by the output pin of each Variable operator. Write access to the signal value is provided by the input pin of the Variable operator.. An attempt to write or set the value of the same signal at multiple operators could produce unexpected results. For example, in the schema fragment below, the same variable signal is set to a value of 5 and to a value of 7. If Design Pad were to process this operator configuration, the signal fValue_m could take on either value---depending on which operator executes last.

Design Pad will issue an error when the same signal is set by multiple Variable operators in the same schema. Note that the same signal may be set to different values in different schemas (if the signal is of module or global scope). This is often desirable, but could lead to unpredictable results similar to the example above. Setting a signal value in multiple locations should always be done with care. In general, it should only be done in mutually exclusive state sub-schemas, or by using the Variable operator's Enable input pin to ensure that the signal is not set to different values at the same time.

Error: Network contains two or more broadcast operators with duplicate signal names. All broadcast operators within a communications network must have unique signal names. This error is issued if the schemas assigned to a network contain two or more broadcast operators with the same signal name. Signal names are case-sensitive, meaning that Design Pad considers OilPressure, oilPressure, and OILPRESSURE to be unique signal names.

Error: Objects form an algebraic loop (use delay elements to implement feedback). Algebraic loops are circular references that cannot be resolved by the Design Pad compiler. For instance, consider the schema shown below, where the output of an Addition operator is fed back to one of its inputs:

The operator output at time t is equal to the sum of its inputs, . And, we have , so the diagram above attempts to compute . But, the computation of the output value cannot be a function of its present value, resulting in an error condition. The correct way to implement feedback is to include a Delay operator in the feedback path, as shown below.

With this arrangement, the output value is a function of its previous value,

Error: Object is not linked to a schema. Function Block and State subschema operators must have a schema associated with them in order to function. Right click on the operator to link a new or existing schema describing the subschema's functionality to the operator.

Error: Operator requires a structure. The user did not select a structure in the operator properties.

Error: Signal connects input pins only. A signal wire represents data flow from one operator to another---the output signal of one operator being fed to the input of another. An input pin of one operator may not feed the input of another operator. This error is issued when an output pin is not part of a wired connection.

Error: Signal is connected to multiple output pins. A signal wire represents data flow from one operator to another--the output signal of one operator being fed to the input of another. The same output signal can be fed to multiple input pins. However, multiple outputs may not be combined to feed the same input. The schema fragment shown below exhibits this error condition. The outputs of the High/Low Alarm operator and of the Logical OR operator are both fed to Relay 1. Since Design Pad cannot discern which output should drive the relay, it issues an error.

Error: Signal wire contains loop. Signal wires should be used to connect operator I/O pins. This error is issued if a schema signal is connected to itself.

Error: Signal Caught during wiring?wire does not connect output pin to input pin. Signal wires should connect the output pin of one operator to the input pin of another. Otherwise, the wire has no effect. Design Pad issues a warning if a signal wire does not make an input/output connection.

Error: State has multiple exit transitions triggered by the same event variable. A State Subschema operator within a state transition diagram has the same variable identified for two or more transitions from that state. Each transition from the state must depend upon a unique variable. Multiple states may use the same transition variable. Double click on the variable name to change what variable triggers the transition.

Error: State transition diagram does not define an initial state, None of the states in a transition is defined as the initial one. Right click on the appropriate state object and select Initial State.

Error: State transition diagram has multiple initial states. More than one of the states in a transition diagram is defined as the initial one. Right click on the appropriate state object and undo Initial State.

Error: Structure library mismatch. The library linked to an operator has changed. The .xml code describing the structure has changed such that it no longer matches the structure described by the operator.

Error: Structure signal mismatch. The connected structures are incompatible. Two operators connected by a signal have chosen different structures.

Error: Structure Variable is linked to incompatible structures. The same variable operator is linked to different structures that have different members.

Error: Sub-schema contains errors. If an operator arrangement within a sub-schema document contains an error, the sub-schema operator that references that sub-schema document is also flagged with an error. The error can only be corrected within the sub-schema document.

Error: Sub-schema links form a loop. The preceding error description identified the problem with algebraic loops. Such circular references could also span operators within a schema and function-block sub-schema. Design Pad issues an error when it identifies an algebraic loop spanning multiple schemas.

Error: Transition is not connected to a state. A state transition diagram has a transition variable specification which is not attached to any state operator.
Warning: Could not check periodic compute times. Design Pad could not check all the schemas' periodic compute times because the "root" processed schema was not periodic.

Warning: Global/Module Variable is being set multiple times. Variable operators serve to store a signal value. Multiple variable operators can reference the very same signal---if they have the same signal name and scope. When the common signal value is set by one operator it is immediately available at all other operators (that reference that signal). If multiple variable operators attempt to set the value of the signal during the same computation loop, results can be unpredictable. Variable operators that reference the same signal should only write the signal value under mutually exclusive conditions (e.g., within mutually exclusive state sub-schemas).

Warning: Object has a connected input pin that is ignored by the operator. The user has connected and input pin on the operator which will not have any effect on schema operation.

Warning: Periodic compute time is less than parent schema's compute rate. The execution of a function block sub-schema depends upon the execution of its parent schema. The sub-schema can only execute when its parent executes---it cannot execute more frequently than its parent. If a sub-schema is configured to compute more frequently than its parent does, it will only execute as frequently as the parent does.

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Warning: Periodic compute time is a not a multiple of parent schema's compute rate. The execution of a function block sub-schema depends upon the execution of its parent schema. The sub-schema can only execute when its parent executes---it cannot execute more frequently than its parent. If a sub-schema is configured for periodic computation, its periodicity should be a multiple of the parent schema's computing periodicity (loop-time). If the parent-schema executes at 100ms intervals, and the sub-schema is configured to execute at 150ms intervals, then the controller will execute the schemas as follows:

Time	Parent Schema Executes?	Sub-Schema Executes?
50ms	No	No
100ms	Yes	No
150ms	No	No
200ms	Yes	Yes
250ms	No	No
300ms	Yes	Yes
400ms	Yes	No
500ms	Yes	Yes
600ms	Yes	Yes

Design Pad will issue a warning when the .sub-schema execution periodicity is not an integer multiple of its parent. Although the controller can execute with such a configuration as indicated in the example above, Design Pad assumes that the designer does not intend to have out-of-phase computation.

Warning: Schema contains a hardware object which is not linked to any hardware resource. Schema documents are hardware independent---they can be associated with different hardware targets. To maintain hardware independence, schemas use generic hardware operators that are subsequently linked to a specific hardware resource. The hardware resource link is stored in the hardware interface document (not the schema document). A generic hardware operator that has not been associated with a specific hardware resource will retain its white background color. Otherwise, its background color will match the title-bar of the module that contains the specific resource it is linked to. Design Pad issues a warning if a generic hardware operator has not been linked to a specific hardware resource. While the controller will be able to execute the schema, results may not be as expected. For example, if an analog input operator is not linked to a specific resource, its output will be 0 (or the low end of the user-defined signal range). If a relay output operator is not linked to a specific relay hardware resource, then no relay will be activated / de-activated by that operator.

Note: Object has one or more unconnected input pins. Certain operators can be processed even if one or more of their input pins are not connected. For instance, the digital input of a Bargraph Display operator need not be connected for a signal to be displayed on a FAC-2000 LED bargraph display. Design Pad issues a note if a pin is not connected, in case the open connection was unintended. (This note is not issued if the object is not used at all. That is, if none of its I/O pins are connected. Most operators that have pins that do not require connections usually have a property setting to show/hide that pin. When the pin is not displayed, Design Pad will not issue this note.)

Note: Object has an unconnected output pin. In general, operator objects generate an output signal based on their inputs. Design Pad will issue a warning if an object has an unconnected output pin and one or more of its input pins are connected. While this condition does not represent an error and the schema can still be executed, it may not have been intended by the schema designer.

Note: Object is not used. Objects that have no I/O pin connections have no effect during schema program execution. Design Pad issues a note if a schema contains any unused objects. These unused objects are optimized out during processing and do not affect controller performance.

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