SINAMICS S120 CDS Backup Control via TB30: Configuration Guide

Architecture Overview: SINAMICS S120 with S7-1500 and TB30 Backup Path

The SINAMICS S120 is a modular drive system commonly paired with a SIMATIC S7-1500 controller over PROFINET using the PROFIdrive profile. In a redundant-standby architecture the drive accepts its primary commands (control word 1, speed setpoint, torque limits, ramp-function generator controls) from the PLC, and a TB30 Terminal Board is installed on the Control Unit (CU320-2 PN or CU310-2 PN) to provide hard-wired digital inputs, digital outputs, and analog I/O that take over if the PLC fails or PROFINET goes down.

Switching between the two control paths is implemented with Command Data Sets (CDS). The drive supports up to four CDS (index 0–3), and the active CDS is selected at runtime by a two-bit binary code written into binector inputs p0810 (bit 0) and p0811 (bit 1). Each CDS carries its own interconnection of the command sources, so CDS0 can be wired to the PROFIdrive receive words coming from the S7-1500 (via p2050, p2051), while CDS1 can be wired entirely to TB30 digital inputs and the TB30 analog input. The PLC toggles p0810/p0811 when a fault condition is detected.

System Topology Diagram

Prerequisites: Hardware, Firmware, and Software

Command Data Set (CDS) Fundamentals

A CDS is a set of binector and connector interconnections stored under a single index. The drive keeps a separate CDS for every control source so that switching between them at runtime does not require parameter re-download. The selection logic is a 2-bit binary word:

For a two-source architecture the PLC only needs to toggle p0810 between 0 and 1, leaving p0811 at 0 permanently. The change is bumpless because the drive reads all CDS values on every scan of the command processing cycle; the active set simply becomes whichever index matches the bit pattern at the time the control word is evaluated.

The number of available CDS depends on the drive object (DO): the Control Unit (DO1) and each Motor Module / Servo drive DO support up to 4 CDS. Drive Data Sets (DDS) are a separate concept and are used to switch encoder configurations, motor data, and closed-loop parameters — not command sources. For this application only CDS is required.

TB30 Terminal Module I/O Specification

The TB30 expands the CU by a fixed I/O set that is independent of PROFINET and therefore available even if the bus is down. Reference: SINAMICS S120 Commissioning Manual.

The TB30 connector pinout on the CU is unique; consult the hardware installation manual for your CU variant before landing conductors. Use shielded twisted pair for the analog channels, with the shield bonded at one end only, typically at the cabinet entry.

CDS Configuration Procedure in STARTER / Startdrive

Perform these steps in order. They assume the project is online with the drive and the CU recognizes the TB30.

1. Insert TB30 in the topology. In STARTER, open the drive navigator, navigate to the CU320-2 PN, right-click the option slot, and select "Insert option board → TB30". Confirm with "OK". Startdrive uses the same path under "Device configuration → option modules".
2. Verify TB30 in the topology tree. Expand the CU and confirm TB30 appears below the option slot. If it does not, click "Update firmware / topology" and re-check the drive's LEDs — a flashing yellow COM LED indicates topology mismatch.
3. Open the expert list. From the drive object, choose "Expert list". Filter the parameter tree by searching for "CDS". You will see parameters with [0], [1], [2], [3] indices, e.g., p0840[0..3].
4. Configure CDS0 (PLC control). In CDS0 — index [0] of every command-source parameter — wire:
   • p0840[0] (ON/OFF1) = r2090.0 (PROFIdrive STW1 bit 0)
   • p0844[0] (OFF2) = r2090.1
   • p0848[0] (OFF3) = r2090.2
   • p0852[0] (enable setpoint) = r2090.6
   • p1070[0] (speed setpoint main) = r2050[1] (NSOLL_A)
   • p1503[0] (torque limit upper) = r2050[2]
   • p1504[0] (torque limit lower) = r2050[3]
5. Configure CDS1 (TB30 backup). Switch the parameter index to [1] using the drop-down next to the parameter name and rewire:
   • p0840[1] = r4022.0 (TB30 DI0 as ON/OFF1)
   • p0844[1] = r4022.1 (TB30 DI1 as OFF2)
   • p0852[1] = r4022.2 (TB30 DI2 as enable setpoint)
   • p1070[1] = r4055[0] (TB30 AI0 as speed setpoint)
   • p1503[1] = fixed value, e.g., p1523 = 80 % (upper torque limit)
   • p1504[1] = p1523 = -80 % (lower torque limit)
6. Set the CDS selector source. On the Control Unit DO, configure:
   • p0810 = r2090.10 (PROFIdrive STW1 bit 10, freely usable per PROFIdrive convention), OR
   • p0810 = a digital input on TB30, e.g., r4022.7 (DI7), if the operator must be able to force CDS1 manually.
   • p0811 = 0 (no need for higher CDS indices)
7. Save and copy RAM to ROM. From the drive toolbar, click "Copy RAM to ROM". Then right-click the drive and choose "Download → to target device".

Parameter Mapping Reference Table

Note that OFF3 in CDS1 is intentionally left at logic 1 (no quick-stop input). If the application requires it, wire TB30 DI4 to p0848[1] via r4022.4.

PLC-Side Implementation in S7-1500

On the S7-1500 side, the PLC maintains a watchdog that toggles the CDS bit if PROFINET diagnostics or a cyclic time-out are detected. A simple pattern in the cyclic OB1:

// Watchdog counter
#iHeartbeat := #iHeartbeat + 1;
IF #iHeartbeat > 1000 THEN
    #iHeartbeat := 0;
    #bHeartbeat := NOT #bHeartbeat;
END_IF;

// Diagnostics-based fallback
#bPLC_OK := NOT "PN-Diag".IO_DeviceFault[0] 
            AND NOT "PN-Diag".ConnectionLoss[0];

// If PLC drops the link, set CDS bit 1 (PROFIdrive STW bit 10)
IF #bPLC_OK THEN
    "DB_Drive".STW1.%X10 := FALSE;      // CDS0 active
ELSE
    "DB_Drive".STW1.%X10 := TRUE;       // CDS1 active
END_IF;

On the hardware, ensure the PLC writes a periodic keep-alive to a configured PROFINET slot so a cable break is detected within ~3 × the configured watchdog time. Siemens PROFINET default in TIA Portal is 3 missed cycles before the device drops out.

Smart Line Module Backup (Infeed Has No CDS)

The Smart Line Module (SLM) and Active Line Module (ALM) do not expose CDS parameters. The infeed's run/enable logic is tied to terminals EP (Enable Pulses) and the 24 V enable rail on the X21 connector. To bring the line module online when the PLC is down:

• Hardware enable approach (recommended). Wire the SLM EP terminal to a 24 V line that is sourced from a UPS or a hardware relay that is energized whenever the cabinet is powered. The SLM will pre-charge and close its line contactor automatically once the DC link is healthy.
• DCC logic approach. Load a DCC chart on the infeed DO that monitors the fieldbus status (r2043.0 = life-sign bit) and drives the infeed enable via the line module's binector input p840[0] on the CU. When the PLC fails, the DCC chart asserts the infeed enable so the DC bus stays powered.
• Manual contactor bypass. For service-mode operation, install a key-switch that bridges the PLC enable relay and connects EP to 24 V. Label clearly and lock out during PLC-controlled operation.

Commissioning Procedure and Verification

1. Power up the cabinet. Confirm the CU's READY LED is green and the TB30 OPT LED is green.
2. Online in STARTER, open the trace and record r0050 (active CDS) and r4022 (TB30 DI status) over 5 s. Force p0810 = 0 and verify r0050 = 0; force p0810 = 1 and verify r0050 = 1.
3. Issue ON/OFF1 from the PLC via the HMI button. Confirm the drive accelerates to the PLC-issued setpoint. Check r0021 (actual speed) matches the setpoint within the ramp.
4. Disconnect the PROFINET cable at the S120 side. Within 3 × watchdog time the drive should report F08501 (PROFINET communication fault) and the PLC's diagnostic block should set bPLC_OK := FALSE. Verify r0050 transitions from 0 to 1 (CDS1 active).
5. Press the backup ON button wired to TB30 DI0. Verify the drive accelerates to the AI0 reference voltage scaled to p2000. With p2000 = 1500 rpm, 5 V at AI0 should give 750 rpm.
6. Toggle p0844 (OFF2) via TB30 DI1 to confirm coast-down.
7. Reconnect PROFINET. The PLC should restore bPLC_OK = TRUE and clear p0810. Acknowledge F08501 from the PLC (or from TB30 DI3 if wired) and confirm CDS0 takes control without a re-start being required.
8. Record the trace during step 7 and confirm r0050 returns to 0 only after the PLC has re-established the cyclic data exchange and acknowledged any faults.

Verification Checklist

• [ ] r0050.0 reads 0 when PROFINET is healthy
• [ ] r0050.0 reads 1 within 1 s of PROFINET failure
• [ ] TB30 AI0 reference at 10 V drives motor to p2000 rpm
• [ ] TB30 DI0 = 1 starts motor with ramp p1120[1]
• [ ] TB30 DI1 = 0 triggers OFF2 within 50 ms
• [ ] Fixed torque limit p1523 is not exceeded at full load (verify with r0080)
• [ ] PLC reconnection automatically restores CDS0 without operator action
• [ ] Infeed DC link r0070 remains within ±5 % of nominal during CDS switchover

Troubleshooting Matrix

Documentation and Reference Manuals

• SINAMICS S120 Function Manual — section 13.5 Data sets (CDS / DDS)
• SINAMICS S120 Commissioning Manual
• SINAMICS Working with Different Data Sets (DDS/CDS)
• SINAMICS S120/S150 List Manual (full parameter reference, includes p0810–p0820 for CDS selection)