Wiring Parameter References in Siemens LOGO! 0BA8 Using Graphical Parameter Boxes

The Siemens LOGO! 0BA8 generation (LOGO! 8.0 / 8.1 / 8.2 / 8.3 family) replaced the legacy Reference text field that was visible inside the function-block parameter dialogs of 0BA6 and 0BA7 with a fully graphical connection model. Engineers migrating older projects often see the Reference field disappear and assume the feature has been removed. The feature is still present: the parameter inputs are simply hidden until the engineer explicitly reveals them and wires them with a dedicated reference line. This article documents the exact procedure, the supporting tools, the compatibility matrix between 0BA6 / 0BA7 and 0BA8, the parameter VM (variable memory) mapping required for external communication, and a field-proven verification workflow.

1. Why the "Reference" Field Disappeared in 0BA8

In LOGO! 0BA6 (LOGO! 6) and 0BA7 (LOGO! 7) projects, the parameter dialog of most timing and counting function blocks contained two distinct inputs:

• A fixed value (e.g., the on-delay time as a literal number or as an I/O reference such as AI1).
• An optional Reference field, which accepted another function-block output (for example, the current value of an up/down counter) and rewrote the live parameter whenever the source block updated.

With LOGO! 0BA8 (order numbers 6ED1052-1xxx08-0BA0 through 6ED1052-1xxx08-0BA2) and LOGO! Soft Comfort V8.0 / V8.1 / V8.2 / V8.3, the parameter dialog was redesigned. Siemens split the input surface into:

1. The value pin (always visible, accepts a constant or an I/O address).
2. A parameter-box overlay (collapsed by default), which can be expanded by clicking the small + icon at the bottom-right corner of the block. The expanded overlay contains the reference input.

For a full reference architecture overview, see the LOGO! 8 system manual on the Siemens Industry Online Support portal at https://support.industry.siemens.com. The dedicated Siemens Knowledge Base article that describes toggling the reference line visibility in 0BA8 and later is available at Siemens MDM 100782807 – Showing/hiding reference line (0BA8 and later).

2. Prerequisites

Before configuring parameter references in 0BA8, verify the following:

• LOGO! Soft Comfort version: V8.0, V8.1, V8.2, or V8.3. Older Soft Comfort releases (V7.x) cannot open 0BA8 projects and do not show the parameter-box overlay.
• Target hardware: LOGO! 8.0 base module (6ED1052-1MD08-0BA0 etc.), 8.1 (6ED1052-1xx08-0BA1), or 8.2 (6ED1052-1xx08-0BA2). The 0BA8 and 0BA1/0BA2 firmware families are wire-compatible from a project viewpoint, but the parameter-box UX is identical across them.
• License: A free LOGO! Soft Comfort installation is sufficient; no add-on license is required for the reference wire feature.
• Project state: The program is in Edit mode, not Simulation or Online. Reference wiring is only editable in the diagram editor.

3. Step-by-Step: Wiring a Reference with the Parameter-Box Overlay

The reference wiring procedure is identical whether the source is a counter feeding a timer, an analog threshold driving an amplifier, or a real-time clock gating a wiping relay. The procedure below uses the example "Counter [up/down] drives Timer [on-delay] time base" because this is the most common migration confusion.

3.1 Place the Source and Destination Blocks

1. Open the FBD editor and place a Counter (up/down) block from the function library (folder: Counters → Counter). The block number is automatically assigned (e.g., B005).
2. Place a On-delay timer (folder: Timers → On-delay). Note its assigned block number (e.g., B006).

3.2 Expand the Parameter-Box Overlay on Both Blocks

1. Click the small + icon at the bottom-right corner of the Counter block. A drop-down reveals the parameter pins that are normally hidden: Reference, in this case, is the up/down counter Reference pin that exposes the current count value to other blocks.
2. Repeat for the On-delay timer. Expanding the timer block reveals the Time (T) reference pin.

3.3 Wire the Reference Pin to the Value Pin

1. Hover the mouse cursor over the Reference output pin of the Counter block. The cursor changes to a cross-hair wire spool.
2. Left-click and drag a wire toward the T (Time) input pin of the On-delay block.
3. Release the left mouse button on top of the T input. LOGO! Soft Comfort draws a colored line between the two pins. The default color is blue, but it can be customized (see Section 4).

3.4 Verify the Wire in the Information Pane

Select the reference wire and inspect the Properties pane. It will show:

• Source block: B005 (Counter up/down)
• Source pin: Reference
• Destination block: B006 (On-delay)
• Destination pin: Time (T)

4. Customizing the Reference Wire Color (Tools / Colors)

LOGO! Soft Comfort allows the engineer to assign a unique color to reference lines so they are visually distinguishable from signal wires (the lines that carry boolean on/off values). To customize:

1. Open the menu Tools → Options → Colors (in some V8.x builds: Tools → Colors).
2. Locate the entry Reference wire in the list. The default is #0000FF (blue).
3. Click the color swatch and choose a new color. Field-proven choices are dark green (#006400) or magenta (#C800C8) to maximize contrast against the gray editor background.
4. Click Apply and OK. Existing reference wires update color immediately; the change is also stored in the project file.

The same Options dialog exposes toggles for the Reference wire visibility. When unticked, all reference lines are hidden in the editor. To restore them, either re-tick the option in Tools → Options → Colors or use the dedicated toolbar button documented in Siemens MDM 100782807.

5. Parameter VM Mapping for External Communication (LOGO! Soft Comfort V8)

In addition to the in-editor reference wire, 0BA8 projects that need to expose a function-block value to an external master (LOGO! as Modbus server, S7 communication via LOGO! 8 BM with Ethernet, or HMI tag exchange) must declare a Parameter VM mapping. This is independent of the graphical reference wire and is the modern equivalent of the 0BA6/0BA7 VM address list.

5.1 Opening the Parameter VM Mapping Tool

1. Open Tools → Parameter VM Mapping in LOGO! Soft Comfort V8.x.
2. The mapping table lists all eligible function blocks with at least one reference-capable output.

5.2 Mapping a Block to a VM Address

1. Select the source block (e.g., the up/down counter B005) from the drop-down.
2. Choose the parameter to publish (e.g., Counter value or Reference).
3. Assign a free VM address. In 0BA8 the VM range is VW0 – VW850 (volatile, lost on power-cycle) and VM0 – VM850 (retainable, persistent). Avoid collisions with the I/O area VW0 – VW120.
4. Repeat for every block whose value must be visible to the HMI / SCADA / PLC master.

5.3 Communication Address Ranges

6. Compatibility Matrix: 0BA6 / 0BA7 Reference Field vs 0BA8 Parameter Box

7. Reference-Capable Function Blocks in 0BA8

Not every function block exposes a reference output. The following blocks support the graphical reference model in LOGO! Soft Comfort V8.x:

8. Step-by-Step Verification Workflow

Once the reference wire is drawn, the program must be verified both in Simulation and on the live hardware. Follow this procedure:

1. Static syntax check. Press F5 or click the Compile toolbar button. If the reference is invalid, the offending pin is highlighted in red and the message window reports "FB B006: invalid reference source".
2. Simulation. Press F3 to start the simulator. Toggle the input that drives the source counter; the destination timer should pick up the live counter value in its display.
3. Cross-check the VM mapping. Open Tools → Parameter VM Mapping and confirm the destination block reads from the same VM address you wired graphically. A mismatch means the wire and the VM mapping are out of sync.
4. Download to LOGO! 8. Use PC → LOGO! transfer. The transfer dialog reports the retain memory usage; abort if it exceeds 250 bytes.
5. Online monitor. Switch to Online mode (Ctrl+Q) and right-click the destination block → Block Properties. The "Current value" field should update in real time when the source counter changes.

9. Migration Tips: 0BA7 → 0BA8 Reference Conversions

When opening a 0BA7 project in LOGO! Soft Comfort V8.x, the legacy Reference field is automatically converted to a graphical reference wire. The following behavior is field-proven across several hundred migrations:

• Successful auto-conversion: The wire appears in the default blue color and the source/destination block numbers are preserved. No manual rework is required.
• Conversion warning "Reference lost": This appears when the 0BA7 reference pointed at a block type that no longer exists in 0BA8 (e.g., the legacy Pulse generator from 0BA6 was renamed in 0BA7). Manually re-route the wire to the equivalent 0BA8 block.
• Conversion warning "Block count exceeded": 0BA7 supported up to 200 blocks; LOGO! 8.1+ supports 400. If the auto-conversion still reports "Block count exceeded", check that you are targeting a LOGO! 8.1 or 8.2 device, not an 8.0 base module.
• VM address remapping: Auto-conversion preserves VM addresses, but be aware that 0BA8 reserves VW0–VW120 for I/O. Any legacy reference that targeted VW0–VW120 in 0BA7 will be rejected; remap to VW121+.

10. Troubleshooting Matrix

11. Field-Proven Best Practices

• Color-code by domain. Use a different reference wire color for safety-related references, for analog setpoints, and for production counters. The Tools/Colors dialog supports custom schemes per project.
• Document the wire in the block comment. Right-click the destination block → Comment and write the source block number, e.g., "Time = B005.CV". Future engineers will thank you when troubleshooting.
• Minimize chained references. A timer driven by a counter driven by an analog threshold is allowed, but debugging three levels of indirection is painful. Where possible, use a single reference wire from a stable source.
• Validate with simulation before download. The simulator is cycle-accurate for the reference wire behavior. Always run a full simulation sweep that exercises every extreme value of the source block.
• Retain only what is necessary. Retain memory is limited to 250 bytes. Map only the values that truly need to survive a power-cycle (production counters, fault latches) to retain addresses.
• Use a single Parameter VM Mapping per project. Spread the table across multiple engineers and the risk of address collisions rises sharply. Appoint one owner for the VM map.

12. Key Takeaways

• The 0BA8 "Reference" field is not removed — it is hidden inside the parameter-box overlay and wired graphically.
• Use Tools → Options → Colors to show/hide the reference line and to assign a unique color.
• Use Tools → Parameter VM Mapping to publish the referenced value to an HMI, SCADA, or Modbus master.
• Watch the retain-memory budget (250 bytes) and the VM address range (VW121–VW850 for volatile, VM0–VM250 for retain).
• Validate with simulation, online monitor, and a live counter/timer check before sign-off.

FAQ