Resolving MC_MoveVelocity ErrorID 8040 on SIMOTICS 1FK7 with S7

Problem Definition: MC_MoveVelocity ErrorID 8040

When a PLCopen MC_MoveVelocity function block is issued from a SIMATIC S7-300T (Technology CPU) against a SIMOTICS S-1FK7 servo motor paired with a SINAMICS S120 / S210 drive, the function block returns ErrorID 8040 if the axis technology object is not in the correct state. The official description from the S7-300T / S7-1500T SIMATIC AX library reads:

"The axis / external encoder are disabled, or the wrong mode is set. The enable signal required for a motion command is missing. Eliminate and acknowledge all queued errors and then enable the relevant axis mode (for example position-controlled)."

This is a state-machine error, not a hardware fault. The motion command is being delivered to the technology object (TO) before the axis has been transitioned from Disabled through Standstill into a mode in which the velocity block is permitted to operate. The same error family and diagnostic logic apply to all PLCopen MC_* motion blocks; the canonical behavior of MC_MoveVelocity is documented in the SIMATIC AX reference at Siemens SIMATIC AX – MC_MoveVelocity: Move axis with velocity/speed setpoint. Although the S7-300T is the older Technology CPU generation, the PLCopen error IDs, axis state model, and required enable sequence are consistent with the S7-1500T Motion Control documentation.

Affected Hardware and Software

Root Cause Analysis

ErrorID 8040 is a symptom, not a fault. Three conditions can produce it on a T-CPU axis:

1. Axis not enabled – MC_Power.Enable is FALSE, the axis is in the Disabled state, or the power-up sequence has not completed. The technology object never reaches Standstill, so any subsequent MC_Home, MC_MoveRelative, or MC_MoveVelocity is rejected.
2. Enable chain not closed at the drive – The SINAMICS terminal enables (EP terminals, STO, OFF1/OFF2/OFF3, drive-specific pulse enable) are missing, so the drive never reports Operation enable and the T-CPU cannot transition the axis into a powered state. The canonical check is the T-DB status word bit 40.0 (DriveEnabled); if it stays 0, the drive is not ready.
3. Wrong axis mode requested – MC_MoveVelocity requires the axis to be in Position-controlled operation by default. If the TO is configured as a pure speed-controlled axis, you must set the PositionControl input of the velocity block to FALSE; otherwise the FB rejects the command with 8040 (or a state-mismatch error depending on firmware revision).

Cross-vendor confirmation: Schneider Electric's EcoStruxure Machine Expert V1.1 PLCO documentation describes the same family of "axis-disabled / wrong mode" errors for its MC_MoveVelocity implementation, listing AccelerationOutOfRange, VelocityOutOfRange, AxisDisabled, and AxisNotReady as the primary causes (see EcoStruxure Machine Expert – MC_MoveVelocity). Rockwell Automation's Micro800 MC_MoveVelocity KB 1156818 maps the same conditions – drive not ready, not in position, axis disabled – to that platform's error class (see Micro800 MC_MoveVelocity ErrorID list). The T-CPU implements the same PLCopen state machine and therefore follows the same diagnostic logic.

Prerequisites

• STEP 7 V5.5 SP4 or later, with the S7-Technology / T-Config option installed and a licensed S7-300T axis object (in the S7-300T licensing model, the TO axis consumes one of the technology object licenses on the CPU's license key).
• Configured TO axis as a positioning axis or synchronous axis (not a pure speed axis) if you intend to use MC_MoveVelocity with the default PLCopen semantics where PositionControl = TRUE.
• PROFIBUS-DP or PROFINET IRT link between the T-CPU and the SINAMICS, fully cyclic, with a configured Siemens standard telegram (typical choices: telegram 105 for a SINAMICS S120 servo with one encoder, or telegram 102 / 103 for S210 PROFINET servo).
• STARTER or Startdrive project loaded, all drive parameters downloaded, and a successful first commissioning on the SINAMICS side – no active F-class faults in the drive fault buffer.
• 1FK7 motor in the SINAMICS motor list with the holding brake configured (e.g., p1215 on S120) and the brake control parameter set matched to the actual brake opening and closing times on the motor nameplate.
• All safety / STO wiring verified: the STO inputs on the SINAMICS Control Unit (X122 / X132 EP terminals on S120 CU320-2, or the PROFIsafe slot on S210) must be energized with 24 V on both channels, or a F-fault will latch and the drive will not release the pulses.

Step-by-Step Diagnostic Procedure

1. Verify the TO type. Open the S7-Technology / T-Config project, select the technology object for axis 1 (and repeat for axis 2), and confirm the type is Positioning axis or Synchronous axis / positioning. A pure Speed-controlled axis is the most common cause of 8040 when PositionControl is left at its default TRUE. If you really want a pure speed axis, change the TO type to Speed axis and set PositionControl = FALSE on the velocity block; in that case only MC_Power, MC_Reset, MC_Stop, MC_Halt, and MC_MoveVelocity can be used on the TO.
2. Open the axis online diagnostics view. In T-Config, right-click the TO and select Axis – Diagnostics. The status word lives in the T-DB at the offsets defined for the SIMATIC AX layout. Confirm the critical bits:
   • Bit 40.0 DriveEnabled = 1 → SINAMICS reports Operation enable and the 24 V / STO chain is closed.
   • Bit 40.1 AxisError = 0 → no TO-level error latched.
   • Bit 40.2 AxisWarning = 0 (or accepted) → no warning blocking the state transition.
   • Bit 40.7 ControlPanelActive = 0 → the T-CPU control panel is not holding the axis; otherwise the MC blocks cannot move the axis.
3. Issue MC_Power with Mode = 0. The block accepts a boolean Enable, an integer Mode (0 = absolute power enable, no advanced qualifiers), a StopMode (0 = standard profile; 1 = emergency stop with maximum dynamic values; 2 = immediate voltage removal / coast), and exposes Status (axis is powered), Busy, Error, and ErrorID. Keep Enable TRUE continuously while debugging. Watch the Status output:
   • Status FALSE after 2-3 s → drive not ready, go to step 4.
   • Status TRUE → go directly to step 5.

   MC_Power
     Enable   := TRUE
     Mode     := 0    // Absolute enable, no advanced mode
     StopMode := 0    // Standard stop profile
     Axis     := Axis_DB1
     Status   => DB1_PowerStatus
     Busy     => DB1_PowerBusy
     Error    => DB1_PowerError
     ErrorID  => DB1_PowerErrorID

4. Issue MC_Reset if Status does not come up. PLCopen reset clears latched axis errors and the cam-disk busy state. Edge-triggered Execute is correct for the first call; in production code, keep Execute TRUE with a watchdog or follow the rising edge of an error signal so a re-triggered fault is also cleared automatically.

   MC_Reset
     Execute := TRUE
     Axis    := Axis_DB1
     Done    => DB1_ResetDone
     Busy    => DB1_ResetBusy
     Error   => DB1_ResetError
     ErrorID => DB1_ResetErrorID

5. Re-check Status. If still FALSE, the problem is on the drive side. Switch to STARTER / Startdrive, open the drive project, and go to Diagnostics – Control Unit. Inspect the drive state word (r0002 / r0046 / r0054 depending on firmware). The drive must report OFF1 = enable, OFF2 = enable, OFF3 = enable, pulses enabled, and ramp-function generator enabled. If the equivalent T-DB bit 40.0 remains 0, the SINAMICS is not ready and the axis can never reach Standstill; no amount of MC-block re-issuing will help.
6. Close the SINAMICS terminal enable chain. On a SINAMICS S120 with CU320-2, the typical safe-torque-off (STO) wiring uses terminals X122.1, X122.2, X132.1, X132.2 (EP) plus a 24 V jumper or two-channel safety output. On a SINAMICS S210, the STO is taken from the PROFIsafe slot; a missing PROFIsafe slot or wrong F-destination address will keep the drive in STO active. Verify the following on every commissioning:
   • STO inputs energized (24 V on both STO channels).
   • No active F-faults (F1611 STO input defective, F1612, F30611, F30885, F08501, F07936 brake ramp, etc.) in the SINAMICS fault buffer.
   • OFF1, OFF2, OFF3 all permissive in the control word (mirror in T-DB). On a Siemens standard telegram 105, the control word 1 bit layout is: 0 = ON/OFF1, 1 = OFF2, 2 = OFF3, 3 = enable pulse, 4 = enable ramp-function generator, 5 = unfreeze ramp, 6 = enable setpoint, 7 = acknowledge fault.
7. Confirm the control word to the drive. From the T-DB layout, locate the control-word mirror (drive telegram offset in the same T-DB). Compare the bits to the SINAMICS state diagram. The canonical sequence is 0x4F7E (ready to switch on) → 0x477E (operation enabled). If you see 0x4740 or 0x4742, the drive is waiting for an enable that the T-CPU is not providing. If you see 0x4F40, OFF2 is missing. If you see 0x4F7C, the setpoint enable (bit 6) is missing – commonly a cam or position-control dependency that has not been satisfied.
8. Issue MC_Home with Mode = 3 (Direct homing, taking the current absolute encoder position as the home position). This is valid for an absolute encoder variant; for an incremental encoder, use Mode = 2 (passive homing using a homing mark) or Mode = 6 (absolute encoder homing only on first power-up). Confirm Done returns TRUE before any move FB is issued. On a T-CPU, MC_Home is a state-changing command; without a successful Done, the axis is not in Standstill and any MC_MoveVelocity will be rejected.
9. Issue MC_MoveVelocity. For a positioning TO, leave PositionControl = TRUE (the default). For a speed-controlled TO, set PositionControl = FALSE. Set Execute = TRUE (latched) and the Velocity input to a non-zero value within the axis dynamic limits. The block then issues a constant setpoint velocity that you can stop with MC_Stop or MC_Halt.

   MC_MoveVelocity
     Execute         := TRUE
     Velocity        := 100.0   // [user units / s] – e.g., mm/s or rev/min
     Acceleration    := 50.0
     Deceleration    := 50.0
     Jerk            := 0.0
     PositionControl := TRUE    // FALSE only for speed-controlled TO
     Axis            := Axis_DB1
     InVelocity      => DB1_VelInVel
     Busy            => DB1_VelBusy
     Error           => DB1_VelError
     ErrorID         => DB1_VelErrorID

Interpreting the 8048 Sub-Fault: "Cam Disk in Use"

After MC_Reset is triggered while the SINAMICS is not yet ready, the T-CPU may surface a different error: ErrorID 8048 with the text "Unable to restart. Restart is only permitted when the axis is disabled. The cam disk is in use by another application and can thus not be reset." This is a latch-conflict error inside the T-CPU technology database, not a SINAMICS drive fault.

Procedure to clear it:

1. Bring the axis fully down: set MC_Power.Enable := FALSE and wait for Status to fall. If the axis was in a cam / synchronization operation, drop the cam first (execute MC_CamIn with Execute := FALSE, or call MC_CamOut on the cam TO).
2. Verify the cam disk resource is released. In T-Config, open the cam technology object (or the cam slot of the positioning TO) and confirm no other FB instance, HMI, or background task has a hold on the cam. The status word of the cam TO carries a CamActive bit; it must read 0.
3. Re-trigger MC_Reset. With the axis Disabled and the cam slot free, 8048 will clear and the error latch will be removed.
4. Re-raise the enable chain: STO → drive enable → MC_Power.Enable := TRUE. Confirm Status = TRUE, then reissue MC_Home, then the velocity command.

1FK7 Integrated Holding Brake: Required Handling

Both motor MLFBs in the original case include an integrated holding brake (the 1DH0 / 1DH5 tail). The 1FK7 holding brake is a 24 V DC, spring-engaged, electrically released brake. If the brake is open-loop controlled from the SINAMICS but the brake-test / brake-control parameters are not fully commissioned, the drive will refuse to release the axis. Typical fault: F07936 "Drive: parking brake ramp not achieved". This in turn keeps T-DB bit 40.0 low and the axis never enters Standstill, so 8040 persists no matter how many times MC_Reset is called.

If you call MC_Power while the SINAMICS holds the brake closed (e.g., because the brake test was aborted or the brake feedback wire is missing), the axis appears "stuck" in T-Config: the PositionActualValue does not update and any motion command returns 8040. Always commission the brake first, then enable the axis.

MC_MoveVelocity Parameter Reference (S7-300T / SIMATIC AX)

Axis State Diagram (PLCopen)

The T-CPU technology object implements the canonical PLCopen motion state machine. The transitions relevant to this error are:

Common T-DB Status Bits to Monitor

Troubleshooting Matrix

Verification Checklist

• With the T-CPU online, open the TO diagnostics view and confirm: status word bit 40.0 = 1, no error, no warning, control panel not active.
• Issue MC_Power.Enable = TRUE and verify Status = TRUE within 2-3 s. If not, the drive side is the bottleneck – do not continue with MC_Home.
• Issue MC_Home with the appropriate mode (3 for direct homing on absolute encoder, 2 for passive homing, 6 for absolute encoder on first power-up). Confirm Done = TRUE and the position actual value matches the expected home coordinate.
• Issue MC_MoveVelocity with a small positive velocity, Execute held TRUE, and PositionControl matching the TO type. Confirm InVelocity rises to TRUE within the configured dynamic limits, and the position actual value advances in the expected direction.
• Issue MC_Halt to ramp down; confirm Done = TRUE and the axis returns to Standstill.
• Repeat for axis 2 (1FK7063-5AH71-1DH5-Z). The same procedure applies; only the motor data block in the SINAMICS differs.

When to Escalate to a Higher-Level Issue

If after completing the verification checklist the axis still reports 8040, the problem is no longer at the MC block level. Open the SINAMICS fault buffer (STARTER → Diagnostics – Fault buffer) and look for F-class faults. Typical candidates on a fresh 1FK7 / S120 install:

• F07015 – Drive: encoder fault. Check the DRIVE-CLiQ / EnDat cable between the 1FK7 and the Sensor Module.
• F07936 – Drive: parking brake ramp not achieved. Brake mechanical issue or p1216 mismatch.
• F30885 – Sensor Module encoder fault. Encoder cable or SM Module replacement.
• F08501 – PROFINET / PROFIBUS communication failure. Check telegram, bus address, slot mapping.

Resolve any F-fault, perform POWER ON of the SINAMICS, and re-run the MC enable sequence.

FAQ