LOGO! 8 Modular Architecture Overview
The Siemens LOGO! 8 (generation 0BA8) is the current modular logic-relay platform for small automation, building-services, and OEM machine applications. A LOGO! 8 system is built from one base (logic) module plus zero or more LOGO! expansion modules snapped to the right-hand side of the base. Digital and analog expansion modules extend the on-board I/O without changing the program, and expansion I/O addresses are mapped consecutively after the base module. The configuration covered here is the most common field combination for LOGO! 8 work:
- Base module: 6ED1052-1FB08-0BA0 — LOGO! 8.2 logic module, 8 DI / 4 DO relay, 24 V DC supply, with display, firmware state 04 (FS04)
- Expansion module: 6ED1055-1FB00-0BA2 — LOGO! 8 DM8 24R digital expansion, 4 DI / 4 DO relay, 24 V DC
- Programming software: LOGO! Soft Comfort V8.0 or later (V8.2 recommended for FS04 support)
System Topology
Decoding the Siemens Order Numbers
Siemens LOGO! order numbers follow a fixed structure. Decoding the part number confirms the generation, variant, and firmware state — the fastest way to verify compatibility before wiring the panel.
| Field | 6ED1052-1FB08-0BA0 (Base) | 6ED1055-1FB00-0BA2 (Expansion) |
|---|---|---|
| Family | 6ED1 = LOGO! | 6ED1 = LOGO! |
| Sub-group | 052 = LOGO! 8 logic module, display variant | 055 = LOGO! 8 expansion module |
| Type code | 1 = Standard logic module | 1 = Digital expansion (DM) |
| I/O code | FB = 8 DI / 4 DO relay | FB = 4 DI / 4 DO relay (DM8 24R) |
| Option / FW state | 08 = FS04, with display (B = display) | 00 = no special options |
| Variant suffix | 0BA0 = 0BA8 standard with display | 0BA2 = released for 0BA2-and-newer base modules (compatible with 0BA8) |
| Power supply | 24 V DC | 24 V DC (fed from base bus) |
| On-board I/O | 8 DI / 4 DO relay | 4 DI / 4 DO relay |
| Output rating | 4 × relay, 8 A resistive | 4 × relay, 5 A resistive |
0BA0 on the base module is a variant code inside the 0BA8 generation, not the original LOGO! 0BA0 device. The original LOGO! 0BA0 Standard had only 6 DI / 4 DO and used a different order-number family (6ED1050-...). A 0BA0 suffix on a 6ED1052-xxx means “0BA8 generation, standard with display.”Compatibility Verification
Q1. Is the DM8 6ED1055-1FB00-0BA2 compatible with the base 6ED1052-1FB08-0BA0?
Yes. The 6ED1055-1FB00-0BA2 is a current Siemens digital expansion module for the LOGO! 8 (0BA8) family. It clips on to the right of the base module and is powered and addressed through the integrated bus connector. No separate supply wiring is needed beyond the 24 V DC field supply at the base. The two modules are a standard, documented combination.
Q2. How do I identify the base module generation?
The generation is encoded in two places:
-
Order number: The
6ED1052-1...family prefix identifies the LOGO! 8 (0BA8) generation. The two-digit code08in the slot before the-0BAxsuffix maps to firmware state 04. The trailing0BA0is the variant (standard with display). - Device label: The top of the unit prints the device family (e.g., “LOGO! 8.2”), the MLFB (full order number), and the FS level.
| Order number family | Generation | Firmware states |
|---|---|---|
| 6ED1050-... (0BA0 suffix) | LOGO! Standard (original) | n/a |
| 6ED1052-1CC... (0BA6) | LOGO! 6 (0BA6) | FS01–FS03 |
| 6ED1052-1HB... (0BA7) | LOGO! 7 (0BA7) | FS01–FS04 |
| 6ED1052-1FB... (0BA8) | LOGO! 8 (0BA8) | FS01–FS06 (6ED1052-1FB08-0BA0 = FS04) |
Q3. Why does LOGO! Soft Comfort show a device named “0BA0” with fewer I/O than the physical hardware?
The device catalog in LOGO! Soft Comfort lists every supported generation. The entry LOGO! 0BA0 refers to the original LOGO! Standard (0BA0 generation) and exposes only 6 DI / 4 DO. The catalog is hierarchical:
- LOGO! 0BA0 — original Standard (6 DI / 4 DO)
- LOGO! 0BA1 — Long variant
- LOGO! 0BA2 ... 0BA7 — intermediate generations
- LOGO! 8 > LOGO! 8.FS1 ... LOGO! 8.FS6 — LOGO! 8 (0BA8) with selectable firmware state
For the 6ED1052-1FB08-0BA0, the correct catalog entry is LOGO! 8.FS4 > LOGO! 8 24RCE (or the display variant matching the hardware). Selecting the wrong generation is the most common cause of the “device found in software has less I/O than physical” symptom.
Selecting the Device in LOGO! Soft Comfort
Use LOGO! Soft Comfort V8.2 or later for FS04 base modules. The procedure below matches the 6ED1052-1FB08-0BA0 to the correct catalog entry and adds the DM8 expansion to the project.
Prerequisites
- LOGO! Soft Comfort V8.2 (or newer 8.x) installed on the engineering PC
- The 6ED1052-1FB08-0BA0 base module, the 6ED1055-1FB00-0BA2 DM8 expansion, and the Ethernet cable (for on-line work)
- A new or existing LOGO! project (.lsc / .lscp file)
Step-by-step — Add the base module
- Launch LOGO! Soft Comfort and open or create a project.
- From the menu, choose
File > Select Hardware...(or the equivalent toolbar button). - In the device tree, expand LOGO! 8 → LOGO! 8.FS4.
- Select the variant that matches the order number: LOGO! 8.2 24RCE with display for 6ED1052-1FB08-0BA0.
- Click OK. The hardware summary now lists 8 DI (I1–I8) and 4 DO (Q1–Q4).
Step-by-step — Add the DM8 expansion
- Open the project diagram. In the toolbar, click Add Expansion (icon: a small block with a ‘+’).
- In the expansion catalog, expand LOGO! 8 > Digital Modules.
- Select DM8 24R (the 4 DI / 4 DO relay module matching 6ED1055-1FB00-0BA2).
- Click Add to Slot 1 (the slot immediately to the right of the base module).
- Confirm the hardware summary now shows 12 DI (I1–I12) and 8 DO (Q1–Q8).
Step-by-step — Configure the connection (for on-line download)
- From
Tools > Ethernet Connections, click Add. - Enter the base module’s IP address (default
192.168.0.3for the first LOGO! 8 on the network). - Click Test Connection. The module’s FS level (e.g., FS04) is reported back.
- Save the connection profile; it is now available for download, run/stop, and online monitoring.
I/O Address Mapping Rules
LOGO! 8 assigns I/O addresses in a fixed, deterministic order: base module first, then expansion modules from left to right. The address space is filled before moving to the next module’s second slot, and analog/digital distinction is handled by the module type, not by a separate address block.
| Position | Module | Digital inputs | Digital outputs | Analog inputs | Analog outputs |
|---|---|---|---|---|---|
| Slot 0 (base) | 6ED1052-1FB08-0BA0 (LOGO! 8.2) | I1 – I8 | Q1 – Q4 | AI1 – AI4 (shared with I1–I4 / I5–I8 on selected variants) | AQ1 – AQ2 (model-dependent) |
| Slot 1 | 6ED1055-1FB00-0BA2 (DM8 24R) | I9 – I12 | Q5 – Q8 | — | — |
| Slot 2 | Next expansion (e.g., DM8) | I13 – I16 | Q9 – Q12 | — | — |
| Slot n | DM16 24 (16 DI / 8 DO) | I(n*4+1) – I(n*4+16) (sequential) | Q(n*4+1) – Q(n*4+8) (sequential) | — | — |
Key conventions for LOGO! 8 (0BA8):
- Digital expansion DM8 (4 DI / 4 DO): adds 4 to the next free I-number range and 4 to the next free Q-number range.
- Digital expansion DM16 (16 DI / 8 DO): consumes 16 I-numbers and 8 Q-numbers in one physical module, but is internally handled as two logical slots of 8 DI / 4 DO each — address assignment is still continuous.
- Analog expansion AM2 (2 AI): maps to the next free AI numbers (e.g., AI3, AI4 on the first AM2).
- Analog output AM2 AQ (2 AO): maps to AQ1, AQ2 (or higher) on the first analog-output module.
- Inputs of the base module can be reused as analog inputs (AI1–AI4 on I1–I8 of variants that support analog). This is selected in the program, not in the hardware configuration.
Maximum System Limits (LOGO! 8 / 0BA8)
LOGO! 8 enforces hard limits on the number of expansion modules and I/O points. Exceeding them prevents the program from running.
| Resource | Maximum | Notes |
|---|---|---|
| Total I/O expansion modules | 24 | Including digital, analog, and communication modules |
| Digital inputs (system-wide) | 24 | 8 from base + 16 from digital expansions |
| Digital outputs (system-wide) | 20 | 4 from base + 16 from digital expansions |
| Analog inputs (system-wide) | 8 | Some shared with digital inputs on the base |
| Analog outputs (system-wide) | 8 | Via AM2 AQ modules |
| AM2 RTD modules | 1 | PT100/PT1000 input |
| Program memory (blocks) | 400 | LOGO! 8.2: up to 400 function blocks |
| Remanent flags | 27 (M1 – M27) | Retained on power cycle |
| Connection resources (S7/Modbus) | 8 S7 + 8 Modbus TCP | Per base module |
Wiring, Power, and Communication
Power wiring (6ED1052-1FB08-0BA0)
- Supply: 24 V DC at the L+ / M terminals (reverse-polarity protected).
- Power consumption: typically 1.7 W with no load on outputs; up to 4.3 W with all relays energized and 24 V on all inputs.
- Use a regulated, isolated 24 V DC supply (Class 2 or SELV). Common references: Siemens LOGO! Power 6EP3330-6SB00-0AY0 (3 A) or 6EP3331-6SB00-0AY0 (6 A).
Input wiring (I1 – I8 on the base, I9 – I12 on the DM8)
- Type: P-type (sourcing), 24 V DC. “ON” threshold ≥ 15 V DC, “OFF” threshold ≤ 5 V DC.
- Sensor current: typically 2.5 mA per input at 24 V DC.
- Common M terminal on the base accepts 0 V returns for all 8 inputs.
- Inputs I1–I8 can be configured in software as digital (I) or analog (AI) on LOGO! 8.2 — see the Soft Comfort program block properties.
Output wiring (Q1 – Q4 on the base, Q5 – Q8 on the DM8)
- Type: relay, NO contacts, isolated.
- Base module rating: 8 A resistive / 2 A inductive per relay, 250 V AC / 30 V DC max.
- DM8 24R rating: 5 A resistive / 2 A inductive per relay, 250 V AC / 30 V DC max.
- Common terminals (L, N for AC, +, − for DC) are pre-wired on the module; the relay contact is a dry SPDT-NO arrangement per output.
- For inductive loads, fit an RC snubber or flyback diode on the load side; Siemens recommends 0.1 µF + 100 Ω for AC and a 1N4007 (or equivalent) for DC coils.
Communication
- Ethernet RJ45 on the base module only. Default IP: 192.168.0.3, subnet 255.255.255.0.
- Supported protocols: S7 communication (PUT/GET), Modbus TCP server, OPC UA server (LOGO! 8.2 and later).
- The DM8 24R expansion has no Ethernet or display — it is invisible to the network except as mapped I/O.
Commissioning and Verification
Verify the configuration before energizing the load side. Power up in this order:
- Confirm 24 V DC supply polarity at L+ / M of the base module with a multimeter before applying power.
- Clip the DM8 24R to the right of the base, ensuring the bus connector seats flush.
- Apply 24 V DC. The base module should boot in 3–5 s and display “LOGO!” on the screen.
- From the on-device menu, navigate to
> Diagnostics > I/O Status. Verify that I1–I12 and Q1–Q8 appear in the status list. If I9–I12 and Q5–Q8 are missing, the DM8 is not detected — re-seat the module. - Force each input by shorting the corresponding input terminal to L+. The status display should toggle to “1” for that input within 100 ms.
- From Soft Comfort, download the program, switch to
RUN, and verify the program executes. Soft Comfort will warn if the program references I/O outside the configured hardware. - Force each output from
Tools > Online Testin Soft Comfort. The corresponding relay should click and the contact should close; verify continuity at the field terminals.
Acceptance check
| Check | Expected result |
|---|---|
| Base boots, no error LED | Green status LED steady; display shows home screen |
| DM8 detected | I/O status menu lists I1–I12 and Q1–Q8 |
| Input test I1–I12 | Status toggles 0 ↔ 1 within 100 ms |
| Output test Q1–Q8 | Relay click heard; continuity closes at terminal block |
| Ethernet reachable | Ping to 192.168.0.3 succeeds; Soft Comfort Test Connection returns OK |
| Program download | Soft Comfort reports successful transfer; LOGO! reboots into RUN |
Troubleshooting Matrix
| Symptom | Likely cause | Fix |
|---|---|---|
| Soft Comfort shows a “LOGO! 0BA0” device with 6 DI / 4 DO | Wrong generation selected in the hardware catalog | Re-open File > Select Hardware and pick LOGO! 8 > LOGO! 8.FS4 > LOGO! 8 24RCE (display)
|
| DM8 not in the I/O status menu | Expansion not clipped fully, or wrong catalog entry (e.g., AM2 selected) | Power off, re-seat the DM8, power on; verify the order number 6ED1055-1FB00-0BA2 matches DM8 24R in the catalog |
| Base reports “No program” after download | Program transferred but RUN was not started | From the device menu, choose Start or set RUN from Soft Comfort |
| Outputs do not energize even though the program runs | Wiring error on the relay contact (no L/N to common terminal) or output forced off | Verify common L (or +) and N (or −) are wired to the output terminal block; clear the force table |
| Bus error: red ERROR LED on base | Expansion bus overloaded (too many modules or insufficient 24 V) | Reduce expansion count; check 24 V supply under load; see the base module manual for the bus error code |
| Ethernet connection fails | Wrong IP, cable issue, or PC on different subnet | Set the PC to 192.168.0.x; replace the patch cable; use Soft Comfort Test Connection
|
| Inputs read 1 even when disconnected | Input wired PNP high without common M, or input jumpered to L+ by mistake | Verify M terminal returns are present; check that the dry contact is between the input and L+, not the input and M |
| Soft Comfort cannot match FS to the connected device | Soft Comfort version older than the device FS | Upgrade Soft Comfort to V8.2 or later; the FS in the catalog must equal the device FS |
Related LOGO! 8 Expansion Modules
The 6ED1055-1FB00-0BA2 is one of several digital and analog expansions for the LOGO! 8 (0BA8) family. Use this quick reference to choose the right part number when extending the system.
| Order number | Description | I/O |
|---|---|---|
| 6ED1055-1FB00-0BA2 | DM8 24R — 4 DI / 4 DO relay | 4 DI / 4 DO |
| 6ED1055-1FB10-0BA2 | DM8 230R — 4 DI / 4 DO relay, 230 V AC supply | 4 DI / 4 DO |
| 6ED1055-1CB00-0BA2 | DM8 24 — 4 DI / 4 DO transistor | 4 DI / 4 DO |
| 6ED1055-1NB10-0BA2 | DM16 230R — 8 DI / 8 DO relay | 8 DI / 8 DO |
| 6ED1055-1MB00-0BA2 | AM2 — 2 AI (0–10 V or 0/4–20 mA) | 2 AI |
| 6ED1055-1MD00-0BA2 | AM2 RTD — PT100/PT1000 input | 2 AI (RTD) |
| 6ED1055-1MM00-0BA2 | AM2 AQ — 2 AO (0–10 V or 0/4–20 mA) | 2 AO |
| 6ED1056-1BP00-0BA2 | CMK2000 communication module (KNX) | network |
Compatibility across generations: a digital expansion marked 0BA2 in the order suffix is compatible with LOGO! base modules from 0BA2 through 0BA8. Mixing a 0BA0 or 0BA1 expansion with a 0BA8 base is not supported by Soft Comfort and will trigger a configuration error.
Frequently Asked Questions
Is the 6ED1055-1FB00-0BA2 (DM8 24R) compatible with the 6ED1052-1FB08-0BA0 base module?
Yes. The 6ED1055-1FB00-0BA2 is the standard 4 DI / 4 DO relay digital expansion for the LOGO! 8 (0BA8) family. It clips to the right of the 6ED1052-1FB08-0BA0 base, is powered from the base bus, and maps its I/O to I9–I12 and Q5–Q8 with no extra configuration.
How do I identify the generation of a LOGO! base module from the order number?
Look at the prefix and the trailing suffix. 6ED1052-1FBxx-0BAx is LOGO! 8 (0BA8). The two digits before the suffix (e.g., 08) encode the firmware state (04 in this case). The original LOGO! 0BA0 Standard uses the 6ED1050-... family with 6 DI / 4 DO and is not the same device.
Why does LOGO! Soft Comfort show a device with fewer I/O than the physical module?
The device catalog lists every generation. The entry labelled “LOGO! 0BA0” is the original Standard with 6 DI / 4 DO, not your LOGO! 8. Open File > Select Hardware, expand LOGO! 8 > LOGO! 8.FS4, and choose the variant that matches 6ED1052-1FB08-0BA0 (LOGO! 8.2 24RCE with display). The hardware summary will then show all 8 DI and 4 DO.
What is the I/O address mapping when a DM8 is the first expansion on a LOGO! 8?
The base occupies I1–I8 and Q1–Q4. The first DM8 24R expansion adds I9–I12 and Q5–Q8. The second expansion continues from I13 and Q9, and so on, in the order the modules are physically mounted from left to right.
How many expansion modules can a LOGO! 8 base support, and what are the hard I/O limits?
Up to 24 expansion modules per base. System-wide maximums are 24 digital inputs, 20 digital outputs, 8 analog inputs, and 8 analog outputs. A typical 24 V DC LOGO! 8 system with a few DM8 and AM2 modules stays well within both the bus and the power budget.