Resolving Siemens MASTERDRIVES A130 Warning in MDI Positioning

Problem Summary

A SIMATIC S7-400 controller (CPU 412-2, order number 6ES7 412-2XG04-0AB0) is communicating with a SIMOVERT MASTERDRIVES MC Plus inverter through a CBP2 PROFIBUS option board in option slot A. The application is configured to run in MDI (Manual Data Input) positioning mode on the drive, with the position setpoint, velocity setpoint, and mode selector being written from the PLC into drive parameters U531, U532, and U533 over PROFIBUS.

All three setpoint words are transferred successfully. The drive reaches operating state r000 = 9 (Ready for switching on), and the control bits OFF1, OFF2, OFF3, and Inverter Enable are all set in the process data control word. When the operator issues a positive edge on the MDI start bit (STA), the drive does not run and immediately returns warning A130 – Operating conditions are not fulfilled. The PLC sees no transition from state 9 into the run-up / run states (14 or 15), and the position register does not change.

The fault is reproducible on every STA edge. It is independent of the actual setpoint values U532 (CFC7 hex) and U533 (4A38 hex) – the drive rejects the move command before either setpoint is processed.

Affected System Configuration

The same recipe fails identically whether the controller is started cold, after a stop, or after a power cycle. The drive's behavior matches the documented A130 condition in the SIMOVERT MASTERDRIVES Compendium, section F01 (positioning).

Root Cause Analysis

A130 is a precondition warning, not a hardware fault. It is raised whenever the user issues a positioning start command while at least one of the following four preconditions is not satisfied:

1. The axis is not yet homed (bit 30 of status word KK315 = 0). For MDI positioning, the MC Plus firmware requires a valid zero reference before any absolute move is accepted. The positioning_status.30 axis_referenced signal must be 1.
2. OFF1 is not edge-controlled. OFF1 (bit 0 of control word 1) must transition from 0 to 1, not be level-held. If the PLC writes 0x047F continuously, the drive never sees a rising edge and stays in "ready for switching on" (r000 = 9).
3. Enable chain not closed. OFF1, OFF2, OFF3, and Inverter Enable must all be 1 at the moment the STA edge occurs. If any one of these is 0, the drive drops back to r000 ≤ 7.
4. Mode mismatch. The drive must echo the requested MDI mode. mode_in = 3 and mode_out = 3 is the correct handshake, but a mode transition in progress (bit transitions in KK315) will momentarily invalidate the start.

In the reported case, points 2, 3, and 4 are already satisfied. The PLC transfers 0x047E first and then 0x047F, r550 shows all four enable bits = 1, r000 is 9, and mode_out = 3 echoes mode_in = 3. The remaining fault is item 1: the axis is not referenced. KK315 bit 30 = 0.

Bit 30 of KK315 is a latched condition. It is cleared at power-on, after a parameter download, after an encoder fault, and after any drive-side reset. The bit only goes to 1 once a complete homing run (active or passive, depending on P570 / P571) has finished successfully and the drive has latched the position reference.

Pre-Start State Verification

Before attempting any MDI move, read the following four parameters from the drive and confirm each is at the expected value:

Decoding r000

The drive state word r000 follows the standard PROFIdrive state diagram. The MDI positioning can only execute from state 15 (Operation enabled, with active positioning).

Decoding r550

r550 is the live mirror of the four most important enable signals. The MASTERDRIVES firmware sets each bit as soon as the corresponding bit in the PROFIBUS control word STW1 is 1. After a successful OFF1 edge you must read:

r550 bit 0  (OFF1)               = 1
r550 bit 1  (OFF2 / no coast stop) = 1
r550 bit 2  (OFF3 / no quick stop)  = 1
r550 bit 3  (Inverter Enable)       = 1

If any of these is 0, the drive will not leave r000 = 9 regardless of how the STA bit is toggled.

Control Word Sequence for OFF1 Edge

OFF1 is a positive-edge-triggered command. The standard sequence for the MC Plus, taken from the SIMOVERT MASTERDRIVES Compendium F01, is:

1. Write STW1 = 0x047E continuously. This sets OFF2 = 1, OFF3 = 1, Inverter Enable = 1, Ramp generator enable = 1, Setpoint enable = 1, and OFF1 = 0. The drive is held in r000 = 4 or r000 = 7.
2. Wait until r000 = 4 (Switch-on inhibit) or r000 = 7 (Switched on). This confirms the inverter has accepted the enable chain.
3. Write STW1 = 0x047F. The single low-to-high transition on bit 0 produces the OFF1 edge. The drive then advances to r000 = 8 (one PLC cycle) and then to r000 = 9 (Ready for switching on).

To stop the drive and reset OFF1, the sequence is reversed:

1. Write STW1 = 0x047F (still running).
2. Wait for the drive to acknowledge the running state.
3. Write STW1 = 0x047E. The high-to-low transition on bit 0 produces a negative edge, which the drive interprets as "OFF1 ramp to stop, then inhibit pulse". The drive decelerates along the configured ramp and returns to r000 = 7.

MDI Mode Parameter Set (U531, U532, U533)

The MC Plus accepts the MDI block in three free parameters, linked by the firmware to the positioning function block:

In the reported case U531 = 0x5B21, U532 = 0xCFC7, U533 = 0x4A38. These values are accepted by the drive without complaint. The drive will still reject the move as long as KK315 bit 30 = 0.

Step-by-Step Resolution

Step 1 – Confirm drive health

Read r000, r550, and any active fault word (typically n_F or n_A list). Resolve all F-class faults first; A-class alarms other than A130 may indicate preconditions that also need to be cleared.

Step 2 – Apply the OFF1 edge

From the PLC, write the control word sequence 0x047E → 0x047F, holding the final value. Verify that r000 advances to 9 and r550 shows all four enable bits = 1.

Step 3 – Run a homing sequence

Trigger the MC Plus homing procedure from the PLC by writing the required mode bits into U531 (with the MDI sub-mode disabled), then producing a positive edge on the homing start bit (commonly STA_HOME, mapped to a control word bit defined by the parameter set). Monitor the drive-side homing status in KK315 bit 30. The bit must transition from 0 to 1 at the end of the homing run.

Step 4 – Verify bit 30 of KK315

After homing, read KK315 and isolate bit 30. If the bit is still 0, the homing run terminated in error. Inspect r000 for the abort reason and check the homing parameter set.

Step 5 – Switch to MDI mode

Write the desired U531 mode bits (sub-mode 00 = absolute, 01 = relative positive, 10 = relative negative) and the setpoint values U532 (position) and U533 (velocity). Wait until the drive echoes the new mode back in KK316 / mode_out.

Step 6 – Start the move

Apply a positive edge to the STA bit. The drive should now leave r000 = 9, run up to operating state 15, and execute the MDI block. Monitor the in-position bit (typically KK315 bit 31) to confirm completion.

PROFIBUS Telegram Layout

For PPO type 3 / 4 / 5 with positioning enabled, the cyclic PZD assignment is typically:

Reading ZSW2/KK315 from the drive and isolating bit 30 is the canonical way for the PLC to know that the drive is ready to accept a MDI block.

Drive State Machine (Inline SVG)

The blue path (r000 = 9 → 14 → 15) is the only valid transition for MDI positioning. The red path represents the A130 return to r000 = 8 / 9 if KK315 bit 30 = 0 when the STA edge arrives.

Verification

After the full sequence completes, perform the following four checks from the PLC program:

1. KK315 bit 30 = 1 (axis referenced) and stays = 1 across drive power cycles and parameter reloads.
2. r000 reaches 15 within one telegram cycle of the STA edge.
3. The actual position (ZSW3 / ZSW4 from the drive) approaches U532 within the configured positioning window and the in-position bit (KK315 bit 31) goes high.
4. A130 is no longer raised. If a fresh A130 appears after a drive-side parameter change, repeat Step 3 – run the homing sequence again.

Record a one-second PROFIBUS trace of the relevant PZD words. The trace should show:

STW1    = 047E 047E 047E 047F 047F 047F 047F 047F 047F 047F
STW2    = 0000 0000 0000 0000 0000 0001 0001 0001 0001 0001   <-- STA edge
ZSW1    = 0C30 0C31 0C32 0C33 0C34 0C34 0C37 0C37 0C37 0C37
ZSW2    = 0000 0000 0000 0000 4000 4000 4000 4000 4000 4000   <-- bit30 sets
r000    = 4    7    8    9    9    9    14   14   15   15

Any deviation from this shape points to either a missing 0→1 edge on STW1 bit 0, a mode handshake still in progress, or a homing abort.

Diagnostic Matrix

Comparison with SINAMICS S120 MDI Semantics

The same A130-equivalent condition exists on SINAMICS S120, but with two notable differences. According to the SINAMICS S120 Function Manual – Drive Functions, MDI mode in the sub-modes "setup mode" and "relative positioning" can be executed without a referenced axis. Only "absolute positioning" requires the axis to be homed. The MASTERDRIVES MC Plus, by contrast, requires a referenced axis for all MDI sub-modes in the standard P570/P571 setup, because the older firmware does not implement the conditional referencing introduced with SINAMICS.

The SINAMICS S120 Basic Positioner Function Manual also introduces a "continuous mode" bit in the MDI control word (bit 5). When set, the inverter continually accepts changes to the position setpoint; relative positioning is disabled in that case. On the MC Plus, continuous-mode behavior is emulated by writing the new setpoint to U532 and re-issuing a STA edge, but the firmware still requires a referenced axis on every start. S7-300/400 examples for relative positioning (mode 4) on TIA Portal are documented in the STEP 7 relative positioning help.

For motion programs that need setup or relative moves without homing, SEW-Eurodrive documents a "sensor-based positioning" mode in the MOVIPRO / MOVIDRIVE positioning manual – useful when migrating a MASTERDRIVES application to a newer platform that allows non-referenced MDI moves.

For network-layer diagnostics unrelated to the drive state machine itself (PROFIBUS cabling, repeaters, MDI/MDIX), the HPE Aruba MDI/MDIX reference covers physical-layer troubleshooting. It is included here only to flag that intermittent A130 in long cable runs can be a symptom of corrupted PZD, not a positioning issue.

Commissioning Checklist

1. Confirm the S7-400 hardware configuration matches the actual rack: CPU 412-2 (6ES7 412-2XG04-0AB0) supports PROFIBUS DP master on the integrated interface; the CBP2 in slot A is addressed as a DP slave at the configured node address.
2. Configure the PPO type. For positioning, PPO type 3 or 5 (with two extra PZD words for the positioning setpoints) is recommended.
3. Set P570 (homing mode), P571 (reference position / LU scaling), and the MDI source parameters (U531 / U532 / U533 links) before going online.
4. Write the control word sequence from a STEP 7 FB so that 0x047E is always written before 0x047F on every start. Hold the 0x047E state for at least one DP cycle before switching.
5. Block the STA edge in the PLC until KK315 bit 30 = 1. The block prevents A130 from cluttering the HMI and protects mechanical components from an un-referenced move.
6. Add a one-second PZD trace to the commissioning archive for each axis. The trace is the fastest way to confirm a clean OFF1 edge and a clean STA edge.

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