Siemens LOGO! 8 CMK2000 Multi-Node HVAC Integration with KTP700

1. Problem Context and System Targets

A typical mid-sized hospitality or office HVAC retrofit calls for centralized scheduling, on-screen unit override, and individual fan-coil control in 40–120 rooms. Siemens' default recipe is a LOGO! 8 base module (e.g. 6ED1052-1MD08-0BA2 or 6ED1052-1MK08-0BA2 for the 230 V KNX variant) wired to RDF600KN/S KNX room thermostats through a CMK2000 communication module, with a KTP700 Basic panel serving as the operator touch screen. When the room count pushes the LOGO!'s variable memory (VM) or its KNX group objects, two recurring questions appear on the integrator's desk:

1. Can a single LOGO! 8 host two or more CMK2000 modules and drive 80+ FCUs?
2. Can two LOGO! 8 controllers (each with its own CMK2000) be presented on a single KTP700 Basic panel?

Both configurations are physically and electrically feasible. Both also carry sharp ceilings that must be budgeted up front so the system ships the first time. The KM-tested ceiling — i.e. the configuration Siemens releases as a system reference — is one CMK2000 per LOGO! 8. Anything above that is the integrator's responsibility, but the LOGO! Soft Comfort toolchain and the KNX stack will not refuse it.

2. Hardware Stack and Order Numbers

3. Architecture Decision Matrix

Architecture B is the most commonly deployed configuration for the requested scope of 80 fan-coil units. The remainder of this reference walks through that path with concrete VM budgeting, KNX object mapping, and HMI networking steps.

4. LOGO! 8 Variable Memory Architecture

LOGO! 8 exposes a single linear VM (Variable Memory) space shared by the user program, the onboard I/O, and the network/communication objects. The total budget is:

• VM total: 850 bytes (firmware ≥ V1.08.x on 0BA2 modules; identical on 0BA1 with caveats for older libraries)
• Network VM: A sub-pool reserved for objects that the LOGO! publishes or subscribes on Ethernet and KNX
• User VM: The remainder used by your FBD program (timers, counters, analog blocks, setpoints)

Each VM entry consumes either 1 byte (Boolean/digital) or 4 bytes (analog/word). When the project crosses 850 bytes the LOGO! Soft Comfort compiler stops with error 0xE001 / "VM memory full". The only remedy is to drop objects, split the project across two LOGO!s, or move analog points to a remote I/O module outside the LOGO! scope.

4.1 VM Budget Worksheet for 80 FCUs

The per-FCU footprint is roughly 12 bytes. For 80 rooms the math breaks the 850-byte ceiling by 110 bytes — that is why Architecture A collapses on a single LOGO! 8. Splitting the rooms 40/40 across two LOGO!s brings each controller to about 480 bytes, leaving a healthy 370 bytes for application logic, scheduler blocks, and global flags.

4.2 Rule-of-Thumb Capacity Curve

FCU count  Single LOGO! VM (bytes)   Status
    10            ~120             OK
    20            ~240             OK
    30            ~360             OK
    40            ~480             OK (Architecture D)
    50            ~600             Tight — drop one analog if possible
    60            ~720             Risk of VM-full compile error
    70            ~840             At ceiling; not safe
    80            ~960             OVER — split to two LOGO!s (Architecture B)
    90           ~1080             Requires three LOGO!s
   100           ~1200             Requires three LOGO!s

5. Network Topology (SVG)

6. LOGO! Soft Comfort Configuration Steps

1. Open the cabinet A program in LOGO! Soft Comfort V8.4. File → New → LOGO! 8.3 (12/24 V).
2. Add CMK2000 to the project tree under Hardware → Right side module → CMK2000. This unlocks the HVAC fan-coil function blocks in the toolbox.
3. Import RDF600KN object list. Use Tools → KNX → Import ETS project (.knxproj) if the KNX topology was authored in ETS; otherwise create group objects manually. Required objects per FCU:\li>
   • RoomTemp — 2-byte float, read-only
   • SetpointShift — 1-byte %, read/write
   • FanStage — 1-byte enum (0=auto, 1=low, 2=med, 3=high)
   • ValveCmd — 1-bit
   • WindowContact — 1-bit
   • Occupancy — 1-bit
4. Build the fan-coil macro by dragging the CMK2000_FCU block from the HVAC library. Each block binds to one RDF600KN. The block auto-publishes the six objects above; check the VM counter at the bottom of the toolbox — it updates live.
5. Repeat for cabinet B with a fresh project file. Use a different IP range suffix (e.g. 192.168.10.12) and a different KNX line address (e.g. 1.1.1 → 1.1.40 for line A, 1.2.1 → 1.2.40 for line B).
6. Compile each project (F12). Watch for warning W017 "VM usage above 80%"; investigate any address flagged yellow.
7. Download via Ethernet. Use Tools → Transfer → Ethernet, target IP, password LOGO by default.

7. CMK2000 Wiring and KNX Topology

The CMK2000 mounts on the right-hand expansion slot of the LOGO! 8 base. Mechanical keying prevents inverted insertion. The two KNX terminals (red/black, polarity-coded) accept the bus cable returning from the RDF600KN daisy chain.

LOGO! 8 base           CMK2000
+-------------+        +----------+
| [I1 I2 ...] |--------| KNX+   -+--------- RDF600KN #1 (red)
|  [CPU+ETH]  |        | KNX-   -+--------- RDF600KN #1 (black)
|             |        |          +--------- RDF600KN #2 (red)
|             |        |          +--------- RDF600KN #2 (black)
+-------------+        +----------+           ... up to 64 devices per line

Maximum KNX devices per CMK2000 line is 64 by KNX specification; the LOGO! CMK2000 stack honours the same ceiling. With 40 FCUs per cabinet the loading factor is ~63%, leaving margin for diagnostics couplers.

8. KTP700 Basic to Multiple LOGO! 8 Controllers

The KTP700 Basic uses WinCC Comfort (TIA Portal) and supports up to four S7 connections simultaneously. Each LOGO! 8 is added as a separate S7 connection. Configure as follows:

1. Add both LOGO! 8 devices in the TIA Portal project tree: Devices & networks → Add new device → PLC → LOGO! 8 → 6ED1052-1MD08-0BA2.
2. Set unique IPs: cabinet A 192.168.10.11, cabinet B 192.168.10.12, KTP700 192.168.10.50. Subnet mask 255.255.255.0.
3. Build the S7 connection in Connections → S7 connection. Slot = 1, rack = 0, partner IP = the LOGO! IP. The LOGO! 8 acts as S7 server only.
4. Map VM tags to HMI variables. The LOGO! 8 exposes VM as DB1 by default in the S7 view. Example mapping for Room 001:

LOGO! VM address     HMI variable                Data type
VW 100              room001_temp                 Real (°C)
VB 110              room001_setpoint_shift       Byte (%)
VB 111              room001_fan_stage           Byte (0–3)
VB 112              room001_valve                Bool
VB 113              room001_window               Bool
VB 114              room001_occ                  Bool

5. Build the faceplate with a 6-cell template (temp / setpoint / fan / valve / window / occupancy) and instantiate it 80 times via the Copy faceplate bulk tool.
6. Add a global scheduler screen that writes occupancy bits at 06:00 / 22:00 via a script or a periodic tag-triggered job.
7. Compile and download WinCC project to the KTP700 over Profinet.

9. Single-LOGO! Multi-CMK2000 Path (Architecture A)

If the integrator still wishes to push Architecture A (one LOGO! 8, two CMK2000, 80 FCUs), the steps are:

1. Mount CMK2000 #1 on the LOGO! base expansion slot (right side).
2. Mount a LOGO! 8 I/O extension module (e.g. DM16 24R) on the right side of CMK2000 to provide a second expansion slot.
3. Mount CMK2000 #2 on the next right-side slot. This is mechanically possible but not in the Siemens-released configuration matrix.
4. Re-import all RDF600KN objects from both lines. The LOGO! Soft Comfort compiler will accept up to ~2 × 64 = 128 KNX devices but will still enforce the 850-byte VM ceiling.
5. Audit VM usage carefully. Because the cabinet architecture is no longer system-tested, the integrator owns the configuration; document the VM map and engineering decision in the as-built file.

10. Commissioning Checklist

1. Power up cabinet A, verify LED state: RUN solid green, KNX solid green.
2. Open LOGO! Soft Comfort → Online → Diagnostic → confirm VM usage matches the offline budget (≈ 480 bytes for 40 FCUs).
3. From the LOGO! display, navigate Network → KNX → Group objects; check each RDF600KN reports a temperature and accepts setpoint writes.
4. Repeat for cabinet B.
5. From the engineering PC, ping 192.168.10.11, 192.168.10.12, 192.168.10.50 — all must reply in < 5 ms on the local subnet.
6. Open WinCC on the engineering station, force a tag read for room001_temp; verify the value matches the physical RDF600KN display within ± 0.3 K.
7. Trigger a setpoint change from the HMI and confirm the RDF600KN screen updates within 2 s.
8. Save the VM map CSV and the WinCC project archive to the project documentation folder.

11. Troubleshooting Matrix

12. Field-Proven Caveats and Best Practices

• Spares model: Keep one spare LOGO! 8 base, one spare CMK2000, and two spare RDF600KN thermostats in stock. Their failure modes are independent.
• VM map versioning: Each VM address should carry a CSV comment exported with every release. Without it, the next engineer cannot map the HMI tag back to the field device.
• KNX line separation: Place the cabinet A and cabinet B KNX lines on physically separate bus cables. Do not share a single KNX segment between the two cabinets — it complicates fault localisation and bypasses the natural 64-device ceiling.
• Firmware lock: Lock the LOGO! 8 firmware at V1.08.x or whatever the project was commissioned with. Firmware upgrades can shift the VM layout.
• Password discipline: Default LOGO! password is LOGO. Change it during commissioning. Keep the new password in the project vault.
• Time schedule: The KTP700 scheduler must be backed up by the LOGO! itself for fail-safe behaviour. A pure-HMI schedule collapses if the panel is rebooted; an on-board scheduler on the LOGO! persists.
• Watchdog: Enable the LOGO! heartbeat (function block B001) and expose it to the HMI as CabA_Heartbeat. If the panel sees a stalled heartbeat, the operator knows the cabinet is hung.

13. HMI Page Layout Recommendations

Design the KTP700 faceplate in three hierarchical screens to keep navigation predictable:

1. Overview — 80 small icons in a 10 × 8 grid. Each icon shows a coloured dot: green (within setpoint band ±1 K), amber (±2 K), red (window open / occupancy override).
2. Room detail — Tapping an icon opens a single-room faceplate with temperature, setpoint slider, fan-speed selector, and override timer.
3. Schedule — Weekly grid with 30-minute slots. Writes occupancy and setpoint-shift bits via an array of VMs.

Keep all 80 rooms addressable from the first two screens; do not require the operator to swipe past sub-menus. The RTP (return-to-page) tag should default to the overview after 60 s of idle.

14. Standards Reference

The integration described here relies on the KNX standard (ISO/IEC 14543-3) for the bus protocol between CMK2000 and RDF600KN, and on the S7 communication model for the Ethernet link between LOGO! 8 and KTP700 Basic. Verify any project-specific overrides against the latest revision of the LOGO! 8 system manual and the CMK2000 product manual before commissioning.