Configuring LOGO! 8.FS4 Software Switch for Display Toggle

Overview: Exposing a Boolean Toggle to the LOGO! Operator

Siemens LOGO! 8.FS4 controllers expose a parameter table that can be navigated from the onboard 6-line display (LOGO! basic units with display) and from the LOGO! TDE external text display. Among the supported parameter types, a single-bit toggle (0/1) is the most frequently requested – for example, an enable/disable flag for a sub-process, a manual override, a maintenance switch, or a feature lock. Although novice users frequently rebuild a toggle with a counter (CNT), a latching relay, or a flip-flop, LOGO!Soft Comfort already provides a purpose-built block for this use case: the Switch (Schalter) function block.

This reference covers the parameter-side configuration of the Switch block, how to publish it into the runtime parameter table, the menu paths on the LOGO! display and the TDE, and the limitations of the "counter-based" workaround that the source question relied on. It is written for control engineers commissioning a stand-alone LOGO! 8.FS4 project (6ED1052-xxx08-0BA1, firmware set 4) using LOGO!Soft Comfort V8.4 or later.

Prerequisites

Verify the configuration environment first:

1. Open LOGO!Soft Comfort and connect the PC to the LOGO! 8 (Tools → Transfer → PC ↔ LOGO!, or Ethernet via "Select Target").
2. Confirm the displayed firmware revision matches "8.FS4". If the device shows an older FS, upgrade with Tools → Transfer → Firmware Update.
3. Open the FBD diagram and locate the parameter list (View → Parameter VM Mapping or double-click a free area in the FBD editor → Parameters tab).

Why a Counter or Flip-Flop Is Not the Right Tool

The source thread opens with a counter that has four parameters (ON, OFF, CNT, STV). Driving the counter’s up/down inputs from the same parameter is functionally acceptable but creates several real-world issues:

• Undefined state risk. If the user assigns both ON and OFF to 1 in the runtime parameter table, the block counts two events within the same LOGO! cycle. Whether the result is a +1, a -1, or no change depends on the cycle order and is not documented as deterministic.
• Parameter overload. A counter exposes four parameters; for a pure toggle only one of them carries meaning. The remaining parameters occupy parameter-table slots and clutter the display menu and TDE.
• Loss of persistence intent. The counter retains the count value across power cycles only if the project uses a retentive flag. The Switch block, by contrast, is designed around a single bit and integrates cleanly with the standard parameter table.
• Display ambiguity. The operator sees a numeric counter value (0, 1, 2, …) rather than a clear "On / Off" status. The TDE and display only translate the raw numeric value; the meaning has to be communicated in a separate legend.

The intended solution – the Switch function block – is a single-bit memory whose state is editable from exactly the same parameter table the user is already using for the analog values.

Locating the Switch Block in LOGO!Soft Comfort

From the editor toolbox in LOGO!Soft Comfort V8.4:

1. Open the instruction palette on the right-hand side of the FBD editor.
2. Navigate to Special → Switch (icon: a single-pole switch).
3. Drag the Switch block onto the diagram and connect its input to a free marker (e.g. M1) or directly to the enable line of the sub-process.

The Switch block has only one parameter that is user-editable: the current state (0 or 1). Internally, the block holds a single retentive bit, so the toggle state survives a power cycle as long as the project has its retentivity settings configured (see File → Properties → Retentivity).

Exposing the Switch State to the Parameter Table

For a parameter to be reachable from the LOGO! onboard display and the TDE, it must be flagged as an "editable parameter" in the parameter table of the project:

1. Select the Switch block in the FBD diagram.
2. Open the Properties dialog (right-click → Properties, or double-click the block).
3. Switch to the Parameters tab. By default the Switch block has a single parameter named On/Off with the values 0 and 1.
4. Click the small checkbox "Operator-controllable" (German: "Bedienbar"). This is the flag that promotes the parameter into the runtime parameter table.
5. Optionally set Visibility to "Show in display" and confirm Selectable is enabled. If the parameter is not selectable, the operator can view but not change the value.

Repeat the operation for every analog value (timer preset, counter threshold, threshold trigger, PI controller setpoint) that the end user must adjust on the display. LOGO!Soft Comfort treats the same flagging mechanism uniformly for every block type, so the source question’s statement that the analog parameters are "working fine" indicates the workflow is already in place.

Runtime Behavior on the LOGO! Onboard Display

On a LOGO! 8 basic with display, navigate to the parameter page:

1. Press ESC until the start screen appears.
2. Press ↓ to scroll to Parameter, then press OK.
3. Use ↑ / ↓ to locate the entry whose label matches the Switch block (default name is the block name, e.g. B001 Switch).
4. Press OK to enter edit mode. The cursor highlights the current value (0 or 1).
5. Press ↑ to set 1, ↓ to set 0 (or use the OK button to toggle, depending on firmware build). Press OK to confirm, then ESC to back out.

The change is written into the Switch block on the next cycle and the program branches accordingly. The display returns to the parameter list with the new value highlighted.

Runtime Behavior on the LOGO! TDE

The LOGO! TDE (6ED1055-4MH08-0BA1) mirrors the same parameter table over Ethernet. Operators typically access it more often than the basic display because of the larger 6-line screen and the cursor keys on a more familiar form factor:

1. From the TDE start screen, select LOGO! → Parameter.
2. Navigate to the Switch block row. The TDE displays both the block name and the current state.
3. Press OK, then use ↑ / ↓ to change 0 ↔ 1.
4. Press OK to commit or ESC to cancel.

The TDE can also be configured to display the parameter on a custom message screen. In LOGO!Soft Comfort, open Tools → Message Configuration (or the "Message text" block in the FBD editor) and add the Switch block’s signal to the message text. The text &Switch1 in the message string resolves to the current 0/1 value at runtime.

Parameter Naming and Display Readability

Default block names such as B001 are not operator-friendly. Rename the block so it is identifiable in the parameter table:

1. Select the Switch block.
2. In the Properties dialog, replace the Comment field with a human-readable name (e.g. Enable Tank 2, Night Mode, Manual Override).
3. Check the Display as name box so the comment, not the block identifier, appears in the menu.

Wiring the Switch Output to the Application

Connect the Switch block’s output to the enable pin of any sub-process – in the source scenario, the "piece of the program" the user wanted to activate/deactivate. Common wirings:

• Enable a motor contactor. Place the Switch output in series with the run output of the function block driving the coil. Q1 = (Run_OK) AND (Enable_Flag).
• Skip a calculation stage. Use a multiplexer (MUX) to feed the Switch output as the selector: MUX_sel = Switch_state.
• Conditional preset for a timer. Feed the Switch state into a threshold trigger’s enable pin so a running timer can be paused without resetting the elapsed value.

(FBD excerpt)
       +--------+
  M1 -->| Switch |--> B001_Switch_out (operator-controllable)
       +--------+
                |
                v
       +--------+
       |  AND   |
       +--------+
          |     |
   Run_OK  |     |  Manual_Fault_Ack (M2)
          v     v
       +--------+
       |   Q1   |  --> Output to drive contactor
       +--------+

Alternative Toggle Implementations (and When They Still Apply)

The Switch block is the correct tool for the source question, but other techniques remain valid for adjacent problems:

Edge Cases and Field-Commissioning Notes

1. Retentivity

By default, the Switch block’s bit is retentive, which means a power-cycle preserves the last operator value. If a project explicitly requires the toggle to default to 0 (Off) on every power-up, open File → Properties → Retentivity and uncheck the Switch block’s entry, or initialize the block in the program with a special-purpose "Initialization" flag triggered by the first cycle after a cold start.

2. Password protection

LOGO! 8.FS4 supports a program password (Tools → Parameter → Access Control). With a password assigned, only the operator level ("Operator" role) can change flagged parameters from the display. If the access level is "Supervisor", the operator can no longer change the toggle without entering the password.

3. Parameter number range

The parameter table is limited in size. With analog values such as timer presets, counter thresholds, and PI controller setpoints, the available parameter slots fill up. The Switch block consumes a single parameter slot, so the trade-off is usually favourable. If the project is approaching the limit, review unused parameters on the View → Parameter VM Mapping table and remove the "Operator-controllable" flag on parameters that should be set in the engineering tool only.

4. TDE network address

The TDE must be on the same IP subnet as the LOGO! 8 and configured to follow the correct master IP. If the TDE shows only a subset of parameters, verify Tools → TDE Settings in LOGO!Soft Comfort and ensure Synchronization is enabled for the parameter table.

5. Firmware 8.FS4 vs. earlier FS

The Switch block has been in LOGO! since the 0BA5 generation. The 8.FS4 revision does not change its parameter-side behavior, but the menu wording and the layout of the Parameter page were refreshed. Users migrating from 0BA7 (LOGO! 7) will notice the new icon, but the edit & confirm sequence is functionally identical.

Verification Procedure

1. Download the modified project to the LOGO! 8.FS4 (Tools → Transfer → PC ↔ LOGO! → Run).
2. On the LOGO! display, navigate to Parameter → locate the Switch block row. Confirm the displayed value is 0 (factory default).
3. Edit the value to 1, confirm, and verify the wired sub-process activates (e.g. observe Q1 turning on if wired to a contactor output).
4. Edit the value back to 0, confirm, and verify the sub-process deactivates.
5. Cycle power on the LOGO! 8 and re-check the value. If retentivity is enabled, the value is preserved; if not, the value resets to 0.
6. On the TDE (if available), repeat the toggle through the TDE menu and verify the state changes propagate identically to the LOGO! display reading.
7. Optional: from LOGO!Soft Comfort in online mode (Tools → Start Online Test), watch the Switch block’s signal in the FBD editor turn red (high) and blue (low) as the value is toggled.

Troubleshooting Matrix

Reference: Switch Block – Quick Specification

FAQ