The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` timer starts counting when `IN` becomes TRUE. The `PT` (Preset Time) is set to 500 milliseconds. The `Q` output becomes TRUE when the elapsed time (`ET`) reaches or exceeds `PT`. The `ET` value is continuously updated as long as `IN` is TRUE.

In the scenario described, the `IN` input is TRUE for 300 milliseconds, then transitions to FALSE. At the moment `IN` becomes FALSE, the `ET` value is 300 milliseconds. Crucially, when the `IN` input of a `TON` function block transitions from TRUE to FALSE, the `ET` value is reset to 0. The `Q` output, which was still FALSE (as 300ms < 500ms), remains FALSE. The timer does not continue counting or hold its value when `IN` goes low. Therefore, after the transition, the `ET` will be 0, and `Q` will be FALSE. The subsequent re-application of a TRUE signal to `IN` will restart the timing process from zero.

The core of this question lies in understanding the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` block is designed to start its timing process when `IN` becomes TRUE. The `PT` (Preset Time) parameter defines the duration for which `IN` must remain TRUE for the `Q` output to become TRUE. Crucially, when `IN` transitions from TRUE to FALSE, the `ET` (Elapsed Time) value is reset to 0, and the `Q` output immediately becomes FALSE, regardless of how much time had elapsed.

Consider a scenario where a `TON` block is configured with `PT` set to 500 milliseconds. The `IN` input is pulsed TRUE for 300 milliseconds, then set to FALSE, and subsequently pulsed TRUE again for 700 milliseconds.

In the first pulse, `IN` is TRUE for 300 ms. Since this is less than `PT` (500 ms), the `Q` output remains FALSE, and the `ET` value reaches 300 ms before `IN` goes FALSE. When `IN` goes FALSE, `ET` is reset to 0.

In the second pulse, `IN` is TRUE for 700 ms. The timing starts again from `ET` = 0. Since 700 ms is greater than `PT` (500 ms), the `Q` output will transition to TRUE after 500 ms of the `IN` signal being TRUE. Therefore, the `Q` output will become TRUE at the 500 ms mark of the second pulse. The `ET` will continue to count up to 700 ms while `IN` is TRUE. The question asks for the state of `Q` at the end of the second pulse, which is after 700 ms of `IN` being TRUE. Since 700 ms is greater than 500 ms, `Q` will be TRUE.

The final state of `Q` at the end of the second pulse is TRUE.

The core concept being tested here is the behavior of bit manipulation functions in IEC 61131-3, specifically the `ROL` (Rotate Left) function, when applied to a WORD data type. A WORD data type in IEC 61131-3 is typically 16 bits wide. The `ROL` function shifts the bits of its first operand to the left by the number of positions specified by its second operand. Crucially, bits shifted off the most significant end are wrapped around and inserted into the least significant end.

Let’s analyze the operation with the given inputs:
Operand 1 (the WORD): `16#A5B3`
Operand 2 (the shift amount): `5`

First, convert the hexadecimal value `16#A5B3` to its binary representation.
`A` in hex is `1010` in binary.
`5` in hex is `0101` in binary.
`B` in hex is `1011` in binary.
`3` in hex is `0011` in binary.

So, `16#A5B3` in binary is `1010 0101 1011 0011`.

Now, perform a Rotate Left operation by 5 positions:
Original: `1010 0101 1011 0011`

Shift 1: `0100 1011 0110 0110` (The leftmost `1` wraps around)
Shift 2: `1001 0110 1100 1101` (The leftmost `0` wraps around)
Shift 3: `0010 1101 1001 1010` (The leftmost `1` wraps around)
Shift 4: `0101 1011 0011 0101` (The leftmost `0` wraps around)
Shift 5: `1011 0110 0110 1010` (The leftmost `0` wraps around)

The resulting binary pattern is `1011 0110 0110 1010`.

Now, convert this binary pattern back to hexadecimal:
`1011` in binary is `B` in hex.
`0110` in binary is `6` in hex.
`0110` in binary is `6` in hex.
`1010` in binary is `A` in hex.

Therefore, the result is `16#B66A`. This understanding is crucial for manipulating bit-level data in PLC programs, such as controlling individual bits within a status word or configuring hardware registers. The `ROL` function is particularly useful when specific bit patterns need to be maintained while shifting their positions, ensuring no data is lost.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` timer starts counting when `IN` becomes TRUE. The `PT` (Preset Time) is set to \(1000\) milliseconds. The `Q` output becomes TRUE when the elapsed time (`ET`) reaches or exceeds `PT`. The `ET` value is continuously updated as long as `IN` is TRUE. When `IN` transitions from TRUE to FALSE, the `TON` timer resets. Specifically, `ET` is immediately set to \(0\), and `Q` becomes FALSE. The question describes a scenario where `IN` is TRUE for \(500\) milliseconds and then transitions to FALSE. Therefore, `ET` will reach \(500\) milliseconds, but it will never reach the preset time of \(1000\) milliseconds before `IN` goes FALSE. Upon the FALSE transition of `IN`, `ET` resets to \(0\). Consequently, the `Q` output will remain FALSE throughout this sequence. The key understanding is that the timer does not “hold” its `ET` value or its `Q` state when the input is de-asserted; it resets. This is a fundamental characteristic of the `TON` block, distinguishing it from other timer types or behaviors. Understanding this reset mechanism is crucial for implementing accurate timing control in PLC applications.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3, specifically concerning its `Q` output and the `ET` (Elapsed Time) output when the input `IN` transitions from TRUE to FALSE. The `TON` block starts counting when `IN` becomes TRUE. The `PT` (Preset Time) defines the duration for which `IN` must remain TRUE for `Q` to become TRUE. The `ET` output continuously reflects the time elapsed since `IN` became TRUE, up to the value of `PT`.

When the `IN` input of a `TON` block transitions from TRUE to FALSE, the `TON` block is reset. This reset action causes the `Q` output to immediately transition to FALSE. Crucially, the `ET` output is also reset to 0. This behavior is fundamental to how timers are used for controlling sequences and ensuring that a condition is met for a specific duration before an action is triggered. If the `IN` signal is removed before the `PT` is reached, the timer effectively aborts its count, and the `Q` output remains FALSE. The `ET` value at the moment of reset is not preserved; it reverts to 0. Therefore, if the `TON` block is configured with a `PT` of 500 milliseconds, and the `IN` signal is active for only 200 milliseconds before going FALSE, the `Q` output will not become TRUE, and the `ET` output will be reset to 0.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3, specifically concerning its `PT` (Preset Time) and `ET` (Elapsed Time) parameters when the input `IN` transitions from TRUE to FALSE. The `TON` block starts counting when `IN` becomes TRUE. The `ET` parameter increments towards the `PT` value. If `IN` remains TRUE for a duration equal to or exceeding `PT`, the `Q` output becomes TRUE. However, if `IN` transitions to FALSE *before* the `ET` reaches `PT`, the `TON` block resets. This reset action causes the `ET` parameter to be immediately set back to its initial value, which is 0. The `Q` output also becomes FALSE. Therefore, when the input `IN` is pulsed for a duration shorter than the `PT` value and then goes to FALSE, the `ET` will not reach `PT`, and consequently, the `Q` output will not activate. The `ET` value will be reset to 0 upon the falling edge of `IN`. This behavior is crucial for implementing timing sequences where a continuous input signal is required for a specific duration to trigger an action. Understanding this reset mechanism is fundamental for accurate timer implementation in control applications.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` timer starts counting when `IN` becomes TRUE. The `PT` (Preset Time) is set to \(500\) milliseconds. The `Q` output becomes TRUE when the elapsed time (`ET`) reaches or exceeds `PT`. The `ET` value is a time value, typically represented as `TIME` data type.

In the scenario described, the `IN` input is TRUE for \(300\) milliseconds and then transitions to FALSE. During the \(300\) milliseconds that `IN` is TRUE, the `ET` value will increment. When `IN` goes to FALSE, the `TON` timer’s behavior is to reset its internal elapsed time counter (`ET`) to \(0\) and its `Q` output to FALSE. Crucially, the timer does not complete its count to \(500\) milliseconds because the input condition was removed before reaching the preset time. Therefore, the `Q` output will remain FALSE, and the `ET` will be reset to \(0\) when `IN` becomes FALSE. The final state of `ET` at the moment `IN` becomes FALSE is \(300\) milliseconds. However, the question asks about the state *after* the transition to FALSE. Upon this transition, `ET` is reset to \(0\).

The correct approach involves understanding the scope and behavior of global variables within the IEC 61131-3 standard, specifically concerning their declaration and accessibility across different program organization units (POUs). Global variables, when declared in a global variable list (GVL), are accessible from any POU within the PLC project. This contrasts with local variables, which are confined to the POU in which they are declared. The standard emphasizes that the scope of a variable dictates its visibility and usability. Therefore, a variable declared in a GVL is inherently available for direct use in Function Blocks (FBs), Functions (FUNs), and Program (PROG) POUs, provided the GVL is properly linked or implicitly available within the project’s compilation context. The key is that the GVL acts as a central repository, making its declared variables universally accessible. This design facilitates data sharing and simplifies the management of system-wide parameters and states. Incorrect options would misrepresent this scope, suggesting limitations that do not exist for GVL-declared variables, such as requiring explicit passing as parameters to every POU or being restricted to only certain types of POUs. The standard’s intent is to provide a mechanism for truly global data access.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3, specifically concerning its `PT` (Preset Time) parameter and the `Q` (Output) signal in relation to the PLC’s scan cycle. The `TON` block starts counting when its `IN` input transitions from FALSE to TRUE. The `ET` (Elapsed Time) variable increments with each PLC scan cycle as long as `IN` remains TRUE. The `Q` output becomes TRUE when `ET` reaches or exceeds `PT`.

Consider a scenario where a `TON` timer has a `PT` of 500 milliseconds. The PLC scan cycle time is 20 milliseconds. If the `IN` input is activated at the beginning of a scan cycle, the `TON` timer will begin accumulating time. The `ET` value will increment by the scan cycle time (20 ms) in each subsequent scan. The timer will reach its `PT` of 500 ms after \( \frac{500 \text{ ms}}{20 \text{ ms/scan}} = 25 \) scan cycles. Therefore, the `Q` output will transition to TRUE at the end of the 25th scan cycle after the `IN` input became TRUE. This means the `Q` output will be TRUE for the duration of the 25th scan cycle and all subsequent cycles as long as `IN` remains TRUE. The crucial point is that the `Q` output becomes active *after* the specified preset time has elapsed, and this timing is synchronized with the PLC’s scan execution. If the `IN` input is de-asserted before `ET` reaches `PT`, the timer resets, and `Q` remains FALSE. The question probes the understanding of this discrete, scan-based timing mechanism rather than a continuous analog behavior.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3, specifically how its `Q` output behaves when the input `IN` transitions from TRUE to FALSE before the preset time `PT` has elapsed. The `TON` function block starts its internal timer when `IN` becomes TRUE. The `Q` output becomes TRUE only when the elapsed time (`ET`) reaches or exceeds the preset time (`PT`). If `IN` transitions to FALSE before `ET` equals `PT`, the timer is reset. This means `ET` is set back to 0, and `Q` becomes FALSE. The `M` (Master Control Relay) logic, often implemented using a `MC` or `MCR` instruction in some PLC architectures, is a separate concept that typically enables or disables blocks of logic. In the context of IEC 61131-3 function blocks, the `TON` block operates independently of any global MCR logic unless explicitly programmed to be influenced by it. Therefore, if the `IN` signal of a `TON` block is de-asserted (goes from TRUE to FALSE) while the timer is still counting, the `TON` block will reset its internal elapsed time and its output `Q` will become FALSE. The presence of a separate `MC` signal, if not directly integrated into the `TON` block’s logic (which is not a standard feature of the `TON` block itself), would not prevent this reset behavior. The `TON` block’s `Q` output is solely dependent on its `IN` and `PT` parameters and its internal elapsed time.

The core concept tested here is the behavior of bit-level operations within IEC 61131-3, specifically focusing on the `R_TRIG` function block and its interaction with boolean variables in a sequential execution environment. The `R_TRIG` function block detects a rising edge of its input signal. When the input `CLK` transitions from FALSE to TRUE, the output `Q` of the `R_TRIG` block becomes TRUE for a single PLC scan cycle. The variable `InputSignal` is a boolean that is set to TRUE at the beginning of the program execution and remains TRUE throughout. The `MyTrigger` variable is an instance of the `R_TRIG` function block. The line `MyTrigger(CLK := InputSignal);` continuously calls the `R_TRIG` block with `InputSignal` always being TRUE. Since `InputSignal` never transitions from FALSE to TRUE, the `CLK` input of `MyTrigger` is always TRUE. Consequently, the `Q` output of `MyTrigger` will never become TRUE because the rising edge condition is never met. Therefore, `OutputState`, which is assigned the value of `MyTrigger.Q`, will remain FALSE. The subsequent `IF MyTrigger.Q THEN` statement will never evaluate to true, and the assignment `OutputState := TRUE;` will never be executed. The final value of `OutputState` will be FALSE.

The core of this question lies in understanding the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` timer starts counting when `IN` becomes TRUE. The preset time is \(PT = T\#5s\). The timer’s output `Q` becomes TRUE when the elapsed time (`ET`) reaches or exceeds \(PT\). The elapsed time (`ET`) is reset to 0 when `IN` becomes FALSE.

Consider the following sequence of events:
1. At time \(t_0\), `IN` transitions from FALSE to TRUE. The timer starts counting.
2. At time \(t_1\), \(t_1 – t_0 = 2s\). `IN` transitions from TRUE to FALSE.
3. At this point, the elapsed time `ET` is \(2s\). Since `IN` is now FALSE, the timer’s internal counter is reset to 0, and the output `Q` becomes FALSE.
4. At time \(t_2\), \(t_2 – t_1 = 3s\). `IN` transitions from FALSE to TRUE again.
5. The timer restarts its count from 0. The preset time is still \(T\#5s\).
6. At time \(t_3\), \(t_3 – t_2 = 4s\). The elapsed time `ET` is now \(4s\).
7. At time \(t_4\), \(t_4 – t_2 = 5s\). The elapsed time `ET` reaches \(PT\). The output `Q` becomes TRUE.

The question asks for the state of the `Q` output at time \(t_4\). Based on the sequence, at time \(t_4\), the timer has completed its 5-second count after the second activation, and therefore, `Q` will be TRUE. The crucial aspect is that the timer resets upon losing its input signal, and the elapsed time does not carry over between separate activations of the `IN` signal. This behavior is fundamental to how `TON` operates to ensure a delay only occurs when the input signal is continuously present for the specified duration.

The fundamental principle being tested here relates to the IEC 61131-3 standard’s definition of function block behavior, specifically concerning the management of internal state and input/output variable propagation across different execution cycles. When a function block is called, its input variables are evaluated. If an input variable is a VAR_INPUT parameter, its value is copied into the function block’s internal scope at the beginning of the execution. Conversely, VAR_OUTPUT variables are updated at the end of the function block’s execution. VAR_IN_OUT variables, however, represent a direct link to the calling scope. Any modification to a VAR_IN_OUT variable within the function block directly affects the variable in the calling scope, and vice-versa, without an explicit copy operation at the start or end of the block’s execution. This behavior is crucial for understanding how data is passed and modified in complex PLC programs, especially when dealing with shared data structures or complex control algorithms. The standard emphasizes that VAR_IN_OUT parameters allow for efficient data sharing and modification, but require careful programming to avoid unintended side effects. The other options describe behaviors that are either incorrect for VAR_IN_OUT parameters or describe the behavior of other variable types (VAR_INPUT, VAR_OUTPUT). Specifically, the idea of a separate internal copy being updated only upon block exit is characteristic of VAR_OUTPUT, not VAR_IN_OUT. The notion of input values being read only once per scan cycle is true for VAR_INPUT, but VAR_IN_OUT offers a more dynamic, bidirectional link.

The core concept being tested here relates to the behavior of function blocks in IEC 61131-3, specifically regarding their state retention and re-initialization. When a Function Block (FB) is instantiated within a program, it maintains its internal state (variables) across PLC scan cycles. This state persistence is fundamental to implementing sequential control, timers, counters, and other memory-dependent logic. However, certain events can trigger a re-initialization of an FB’s internal variables. In the context of IEC 61131-3, the primary mechanism for explicitly resetting an FB’s state is through the use of the `R_TRIG` (Rising Edge Trigger) or `F_TRIG` (Falling Edge Trigger) function blocks, or by explicitly calling a reset method if the FB supports one. More broadly, if an FB is declared within a program organization unit (POU) that is itself re-initialized (e.g., a task that is stopped and restarted, or a specific program block that is re-executed from its beginning under certain conditions), the FB’s internal variables will also be reset to their initial declared values. The question focuses on the implicit behavior of an FB’s state persistence when its containing POU is executed repeatedly in a normal scan cycle, without any explicit reset mechanism being activated. In such a scenario, the FB’s internal variables retain their values from the previous scan cycle. Therefore, if an FB’s internal counter variable, `Count`, was incremented to 5 in the previous scan, it will still be 5 at the beginning of the current scan, unless an explicit reset action occurs. The question describes a situation where the FB is called repeatedly in the main task, and no external reset signal is applied. Consequently, the internal state of the FB, including its counter, will persist. If the counter was previously incremented to 5, it will remain 5 until a reset condition is met. The correct understanding is that the FB’s state is preserved between calls within the same scan cycle and across subsequent scan cycles as long as the containing POU is active and no reset is triggered.

The core concept being tested here is the behavior of the `TON` (Timer On-Delay) function block in IEC 61131-3 when its `IN` input transitions from TRUE to FALSE. The `TON` block starts its timing when `IN` becomes TRUE. The `Q` output becomes TRUE when the preset time (`PT`) has elapsed and `IN` is still TRUE. The `ET` (Elapsed Time) output continuously increments as long as `IN` is TRUE, up to the value of `PT`.

In the given scenario, the `TON` block is instantiated with `PT` set to \(1000\) milliseconds. The `IN` input is pulsed TRUE for \(500\) milliseconds and then immediately set to FALSE.

1. **Initial State:** `IN` is FALSE, `Q` is FALSE, `ET` is \(0\).
2. **First Transition:** `IN` becomes TRUE at time \(t=0\). The timer starts counting.
3. **During the Pulse:** For the duration of \(500\) milliseconds, `IN` remains TRUE. The `ET` output will increment from \(0\) to \(500\) milliseconds. Since \(500\) milliseconds is less than the preset time of \(1000\) milliseconds, and `IN` is still TRUE, the `Q` output remains FALSE.
4. **Second Transition:** At time \(t=500\) ms, `IN` transitions from TRUE to FALSE.
5. **Timer Reset:** According to the IEC 61131-3 standard for the `TON` function block, when the `IN` input transitions from TRUE to FALSE, the timer is immediately reset. This means the `ET` output is reset to \(0\), and the `Q` output is reset to FALSE, regardless of the current value of `ET` or whether `PT` had been reached.

Therefore, after the \(500\) ms pulse, the `ET` output will be \(500\) ms, and the `Q` output will be FALSE. The timer does not complete its cycle because the `IN` signal was removed before the preset time elapsed, and the reset action occurs upon the falling edge of `IN`. The key is that the `TON` block requires `IN` to remain TRUE for the entire duration of `PT` for `Q` to become TRUE, and any interruption of `IN` before `PT` elapses, or a transition of `IN` to FALSE, will reset the timer.

The core concept being tested here is the behavior of the `R_TRIG` function block in IEC 61131-3 when its input signal transitions from TRUE to FALSE. The `R_TRIG` block detects a rising edge, meaning it sets its output Q to TRUE for one PLC scan cycle when its input CLK transitions from FALSE to TRUE. In this scenario, the input CLK is held TRUE for an extended period, and then transitions to FALSE. The `R_TRIG` block’s Q output will only become TRUE when CLK transitions from FALSE to TRUE. Since CLK is continuously TRUE and then becomes FALSE, there is no rising edge detected. Therefore, the Q output will remain FALSE throughout the execution cycle where CLK is FALSE. The question probes the understanding that `R_TRIG` is specifically for rising edge detection and does not react to falling edges or sustained TRUE states. This is a fundamental aspect of edge detection function blocks and their proper application in PLC programming for event-driven logic. Understanding this behavior is crucial for implementing reliable control sequences that respond to specific state changes rather than continuous conditions.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3, specifically its interaction with the `IN` (Input) and `Q` (Output) signals, and the role of the `PT` (Preset Time) parameter. When the `IN` signal transitions from FALSE to TRUE, the `TON` timer begins counting. The `ET` (Elapsed Time) variable increments at a rate determined by the PLC’s scan cycle and the PLC’s system clock resolution, up to the value specified by `PT`. The `Q` output becomes TRUE only when `ET` reaches or exceeds `PT`. Crucially, if the `IN` signal transitions back to FALSE *before* `ET` has reached `PT`, the timer is reset. This means `ET` is set back to 0, and `Q` becomes FALSE. The question describes a scenario where the `IN` signal is pulsed for a duration less than the `PT` value. Therefore, the `ET` will not reach `PT`, and consequently, the `Q` output will remain FALSE. The `ET` value at the end of the scan cycle where `IN` goes FALSE will be less than `PT`. The correct understanding is that the timer requires a continuous TRUE state on its `IN` input for a duration equal to or exceeding `PT` to activate its `Q` output. Any interruption of the `IN` signal before this preset time elapses will cause the timer to reset, preventing the `Q` output from becoming TRUE. This behavior is fundamental to implementing delay functions in automation.

The core concept being tested here is the behavior of the `R_TRIG` function block in IEC 61131-3 when its input signal transitions from TRUE to FALSE. The `R_TRIG` block detects a rising edge, meaning it sets its output Q to TRUE for one PLC scan cycle when its input CLK transitions from FALSE to TRUE. When the input CLK transitions from TRUE to FALSE, the `R_TRIG` block’s internal state is reset, and its output Q remains FALSE. Therefore, if the input CLK is continuously TRUE, the `R_TRIG` block will not trigger its output Q. The question describes a scenario where the input CLK of an `R_TRIG` instance is held TRUE. In this state, no rising edge is ever detected by the `R_TRIG` block. Consequently, the output Q will remain FALSE throughout the execution of the program. This understanding is crucial for implementing event-driven logic and ensuring predictable behavior in PLC control systems. It highlights the importance of understanding the state transitions and edge detection mechanisms provided by standard function blocks.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` block starts its internal timer when `IN` becomes TRUE. The output `Q` becomes TRUE when the preset time `PT` has elapsed and `IN` is still TRUE. The elapsed time `ET` is continuously updated to reflect the time passed since `IN` became TRUE.

When `IN` transitions from TRUE to FALSE, the `TON` function block immediately resets. This means its internal timer is stopped, and the elapsed time `ET` is reset to 0. Crucially, the output `Q` also immediately becomes FALSE. The preset time `PT` remains unchanged unless explicitly modified by another part of the program. Therefore, if the timer had not yet reached its preset time when `IN` went FALSE, the output `Q` will not have become TRUE. The timer’s state is effectively discarded upon the falling edge of `IN`.

Consider a scenario where `IN` is TRUE for 500 milliseconds, and `PT` is set to 1000 milliseconds. During this 500ms, `ET` would increment from 0ms to 500ms, and `Q` would remain FALSE. If `IN` then transitions to FALSE, `ET` immediately resets to 0, and `Q` becomes FALSE. The timer does not “remember” that it had accumulated 500ms of ON time. The next time `IN` becomes TRUE, the timer will start counting from 0 again. This behavior is fundamental to understanding how to implement timing sequences in PLC programming.

The core concept tested here is the behavior of bit manipulation functions in IEC 61131-3, specifically the `SET` and `RESET` operations on bit elements within a word or array. When a bit within a word is addressed using an index (e.g., `WORD_VAR.5`), it refers to the bit at that specific position. The `SET` function, when applied to a specific bit, forces that bit to a logic ‘1’ state, irrespective of its current value. Conversely, the `RESET` function forces a specific bit to a logic ‘0’ state.

Consider the initial state: `WORD_VAR` is initialized to `16#00FF` (binary `0000 0000 1111 1111`).
The first operation is `SET(WORD_VAR.5)`. Bit 5 (counting from 0 on the right) of `WORD_VAR` is currently ‘0’. Applying `SET` changes this bit to ‘1’. The word becomes `0000 0000 1011 1111` (binary), which is `16#00BF`.
The second operation is `RESET(WORD_VAR.2)`. Bit 2 of `WORD_VAR` is currently ‘1’. Applying `RESET` changes this bit to ‘0’. The word becomes `0000 0000 1011 1011` (binary), which is `16#00BB`.
Therefore, the final value of `WORD_VAR` is `16#00BB`.

This scenario highlights the importance of understanding bit-level access and the atomic nature of `SET` and `RESET` operations on individual bits within IEC 61131-3 data types. It’s crucial to recognize that these operations modify the specified bit without affecting other bits in the word, and the order of operations matters. Advanced PLC programming often involves intricate bit manipulation for efficient control and status management, making a thorough grasp of these fundamental functions essential for developing robust and predictable automation logic. Understanding the underlying binary representation and how functions interact with it is key to debugging and optimizing code.

The correct approach involves understanding the scope and behavior of function blocks in IEC 61131-3, particularly concerning their instantiation and state management. When a function block is called within a program organization unit (POU) that is executed cyclically, each call to the function block, if it is not explicitly declared as a global variable list or within a specific scope that persists across POU executions, will result in a new instance being created. This new instance will have its internal variables initialized according to their declarations. If the function block is intended to maintain its state across multiple scans of the cyclic POU, it must be instantiated in a scope that persists, such as a global variable list or as a VAR_GLOBAL INSTANCE. Without such persistent instantiation, each execution of the POU that contains the function block call will effectively create a fresh, uninitialized instance of that function block, leading to its internal state being reset with each cycle. Therefore, to ensure the function block’s state is preserved across program cycles, it must be declared and instantiated in a manner that guarantees its existence and memory retention beyond a single POU execution. This is a fundamental concept for managing stateful logic in PLC programming.

The core concept tested here is the behavior of function blocks in IEC 61131-3, specifically regarding their state persistence and re-initialization. When a function block is called within a program organization unit (POU) that is executed cyclically, its internal state (variables declared within the function block’s scope) is preserved between calls. This persistence is fundamental to implementing stateful logic, such as counters, timers, or control algorithms. However, if the function block instance itself is declared within a POU that is only executed conditionally or not at all during certain program cycles, its internal variables will retain their last known values. The question describes a scenario where a function block instance, `FB_ProcessData`, is declared globally and called within the `PROGRAM_MAIN` POU, which executes cyclically. The `FB_ProcessData` has an internal timer `TON_Delay` and a boolean output `Q_Ready`. The `TON_Delay` is configured with a preset time of 5 seconds. The input `I_Start` triggers the timer. When `I_Start` transitions from FALSE to TRUE, the timer begins counting. If `I_Start` remains TRUE for the full 5 seconds, `Q_Ready` becomes TRUE. The critical aspect is what happens when `I_Start` is TRUE for only 3 seconds and then becomes FALSE before the timer completes its preset. In this case, the `TON_Delay` function block will not have its `Q` output transition to TRUE. Crucially, because the function block instance is globally declared and `PROGRAM_MAIN` is cyclic, the internal state of `FB_ProcessData` and its `TON_Delay` instance is preserved. When `I_Start` becomes TRUE again in a subsequent cycle, the timer will resume counting from its current elapsed time, not from zero. Therefore, if `I_Start` is TRUE for 3 seconds, then FALSE, and then TRUE again, the timer will only need an additional 2 seconds of `I_Start` being TRUE to reach its 5-second preset and activate `Q_Ready`. This means `Q_Ready` will become TRUE after a total of 5 seconds of `I_Start` being TRUE, regardless of interruptions. The question asks for the state of `Q_Ready` after `I_Start` has been TRUE for 3 seconds, then FALSE for 2 seconds, and then TRUE again for 2 seconds. The timer accumulates 3 seconds, is reset by the FALSE transition of `I_Start` (as per standard TON behavior when the input goes false), and then starts counting again from 0 for 2 seconds. Thus, `Q_Ready` will remain FALSE.

The scenario describes a PLC program that utilizes a Function Block (FB) named `MOTOR_CONTROL` with an internal state variable `_state`. The FB has an input `START` and an output `RUNNING`. The logic within the FB transitions the `_state` variable based on the `START` input. Specifically, when `START` is TRUE, the `_state` variable is set to `RUNNING`. When `START` is FALSE, the `_state` is set to `STOPPED`. The `RUNNING` output is directly mapped to the `_state` variable.

The core concept being tested here is the behavior of Function Blocks in IEC 61131-3, particularly regarding instance data and state management across multiple calls within a single PLC scan cycle. When a Function Block is called multiple times within the same scan, each call operates on the *same* instance of the FB. Therefore, any internal variables, such as `_state`, retain their values from the previous call within that scan cycle.

In the given scenario, the first call to `MOTOR_CONTROL` with `START` as TRUE will set `_state` to `RUNNING` and `RUNNING` output to TRUE. The second call to `MOTOR_CONTROL` with `START` as FALSE will then execute. Because the `_state` variable is still `RUNNING` from the previous call, the condition `START` is FALSE will be met, and `_state` will be updated to `STOPPED`. Consequently, the `RUNNING` output will also become FALSE. This demonstrates that the FB’s internal state is persistent across calls within a scan, and subsequent calls can modify this state based on new input conditions. The final state of the `RUNNING` output will reflect the outcome of the *last* call to the FB within that scan cycle.

The core concept being tested here is the behavior of the `TON` (Timer On-Delay) function block in IEC 61131-3 when its `IN` input transitions from TRUE to FALSE. The `TON` block starts its timing process when `IN` becomes TRUE. The `PT` (Preset Time) is set to \(T\#5s\). The `Q` output becomes TRUE only when the accumulated time (`ET`) reaches or exceeds `PT`. The `M` (elapsed time) output continuously updates with the accumulated time.

In the given scenario, the `IN` input is TRUE for \(T\#2s\) and then transitions to FALSE. At the moment `IN` becomes FALSE, the `TON` function block stops accumulating time and, crucially, resets its internal `ET` value to \(T\#0s\). The `Q` output, which was FALSE because \(ET\) (\(T\#2s\)) had not yet reached `PT` (\(T\#5s\)), remains FALSE. The `ET` output also resets to \(T\#0s\). Therefore, after the `IN` input goes to FALSE, the `ET` will be \(T\#0s\).

This behavior is fundamental to understanding how timers operate in IEC 61131-3. Unlike a timer that might hold its accumulated value upon disconnection, the `TON` block’s specification dictates an immediate reset of `ET` when the enabling input is de-asserted. This ensures predictable behavior for timing sequences that require a fresh start upon re-activation. Understanding this reset mechanism is vital for implementing accurate timing control in automation systems, preventing unexpected delays or incorrect state transitions.

The scenario describes a PLC program that utilizes a Function Block (FB) named `MOTOR_CONTROL` which has an internal state variable, `_MotorState`. This variable is of type `INT` and is intended to represent different operational modes of a motor. The FB is instantiated within a Structured Text (ST) program. The question probes the understanding of how to correctly access and modify this internal state variable from outside the FB’s scope, specifically within the calling program. According to IEC 61131-3:2013, internal variables of a Function Block, often referred to as instance variables or private variables, are not directly accessible from outside the FB’s definition unless explicitly exposed through VAR_OUTPUT or VAR_IN_OUT declarations. In this case, `_MotorState` is declared within the `VAR` section of the `MOTOR_CONTROL` FB, making it an internal variable. Therefore, attempting to directly assign a value to `_MotorState` from the calling ST program, as if it were a global variable or a public output, is syntactically incorrect and will lead to a compilation error. The correct method to influence or read the internal state would involve defining appropriate input or output variables in the FB’s interface and using those for communication. For instance, an input variable could be used to set the desired state, and an output variable could be used to read the current state. Without such an interface, direct external manipulation of `_MotorState` is prohibited by the standard’s encapsulation principles for FBs.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input `IN` transitions from TRUE to FALSE. The `TON` timer starts counting when `IN` becomes TRUE. The `PT` (Preset Time) is set to 500 milliseconds. The `Q` output becomes TRUE when the elapsed time (`ET`) reaches or exceeds `PT`. The `ET` value is continuously updated as long as `IN` is TRUE.

In this scenario, `IN` is TRUE for 300 milliseconds, and then it transitions to FALSE. At the moment `IN` becomes FALSE, the `TON` timer stops counting, and its internal `ET` value is frozen at the elapsed time it had reached. Since `IN` was TRUE for only 300 milliseconds, and the `PT` is 500 milliseconds, the `Q` output will never become TRUE because the timer did not complete its count. Crucially, when `IN` transitions from TRUE to FALSE, the `ET` value is reset to 0. Therefore, after the transition to FALSE, the `ET` will be 0.

The question asks about the state of `ET` *after* the input `IN` has transitioned from TRUE to FALSE. Based on the IEC 61131-3 standard for the `TON` function block, when the `IN` input transitions from TRUE to FALSE, the timer’s internal elapsed time (`ET`) is reset to 0. This reset occurs regardless of how long `IN` was previously TRUE, as long as it was less than the preset time `PT`. The `Q` output remains FALSE because the preset time was not reached.

The core concept being tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input is repeatedly pulsed with a duration shorter than the preset time. The `TON` timer starts its internal counter when its input (`IN`) transitions from FALSE to TRUE. The `Q` output becomes TRUE only when the internal elapsed time (`ET`) reaches or exceeds the preset time (`PT`). If the `IN` input transitions back to FALSE before `ET` reaches `PT`, the timer resets, and `ET` returns to 0.

In the described scenario, the `IN` input is pulsed with a period of 50 ms, and the `PT` is set to 100 ms. Each pulse lasts for 20 ms.
– **Pulse 1:** `IN` goes TRUE at t=0 ms. `ET` starts counting. At t=20 ms, `IN` goes FALSE. The timer resets, `ET` becomes 0 ms. `Q` remains FALSE.
– **Pulse 2:** `IN` goes TRUE at t=50 ms. `ET` starts counting from 0. At t=70 ms, `IN` goes FALSE. The timer resets, `ET` becomes 0 ms. `Q` remains FALSE.
– **Pulse 3:** `IN` goes TRUE at t=100 ms. `ET` starts counting from 0. At t=120 ms, `IN` goes FALSE. The timer resets, `ET` becomes 0 ms. `Q` remains FALSE.

Since the duration of each pulse (20 ms) is less than the preset time (100 ms), and the time between pulses (30 ms) also causes the timer to reset before it can accumulate enough time, the `ET` never reaches `PT`. Consequently, the `Q` output will never transition to TRUE. The `ET` value will always be reset to 0 ms at the end of each pulse. Therefore, the `ET` will never reach 100 ms.

The core concept tested here is the behavior of the `TON` (Timer On Delay) function block in IEC 61131-3 when its input signal transitions from TRUE to FALSE. The `TON` block starts its timing process when its `IN` input becomes TRUE. The `PT` (Preset Time) parameter defines the duration for which the `IN` input must remain TRUE for the `Q` output to become TRUE. Crucially, if the `IN` input transitions from TRUE to FALSE *before* the `Q` output becomes TRUE (i.e., before the preset time has elapsed), the timer is reset. This means the internal elapsed time (`ET`) is also reset to 0, and the `Q` output reverts to FALSE.

In the given scenario, the `TON` block is configured with a `PT` of 500 milliseconds. The `IN` input is pulsed for 300 milliseconds. Since 300 milliseconds is less than the preset time of 500 milliseconds, the `IN` input becomes FALSE before the timer can complete its cycle and activate the `Q` output. Consequently, the `TON` block resets. The `Q` output will remain FALSE, and the `ET` value will be reset to 0. Therefore, after the pulse, the `Q` output will be FALSE and the `ET` will be 0.

The core of this question lies in understanding the behavior of the `R_TRIG` function block in IEC 61131-3 when its input signal transitions from FALSE to TRUE. The `R_TRIG` block is designed to detect a rising edge. When the input `CLK` transitions from FALSE to TRUE, the output `Q` of the `R_TRIG` block becomes TRUE for a single PLC scan cycle. Subsequently, if the `CLK` input remains TRUE in the next scan, the `Q` output will be FALSE. The `M` output of `R_TRIG` is TRUE only during the scan cycle when the rising edge is detected. Therefore, in the given scenario, the `CLK` input transitions from FALSE to TRUE at the start of scan cycle 1. This causes `Q` to become TRUE and `M` to become TRUE during scan cycle 1. In scan cycle 2, `CLK` remains TRUE, but since there is no rising edge (it was already TRUE), both `Q` and `M` will be FALSE. The question asks for the state of the `Q` output in scan cycle 2.