1. Problem Statement: MM420 Reports F0060/F0070 on DriveMonitor Online Connection
When a Siemens MICROMASTER 420 (MM420) inverter is brought online through DriveMonitor using the PC RS232 connection kit (6SE6400-1PC00-0AA0), the parameter list is read successfully, but a fault remains latched in the drive. The fault shows up in parameter r0947 (last fault number) and r0948 (fault value). Typical reported values are F0060 and F0070. The fault will not clear while DriveMonitor is online, even after the operator presses the reset button on the Basic Operator Panel (BOP), and it re-appears every time the drive powers up in remote configuration.
This symptom is almost always related to a Communications Board (CB) telegrams-failure condition caused by removing the Profibus (or other fieldbus) module and substituting the PC RS232 kit. The drive continues to expect a cyclic setpoint from the fieldbus because its control source is still configured for CB, and the resulting telegram timeout trips F0070. F0060 frequently appears as a secondary fault when the ASIC watchdog inside the drive detects the inconsistent comms state.
2. Understanding r0947, r0948, and the MM420 Fault Buffer
The MM420 stores faults in a small circular buffer accessible through read-only parameters. Knowing exactly what each parameter means prevents confusion when DriveMonitor displays multiple fault codes at once.
| Parameter | Name | Description |
|---|---|---|
| r0947[0] | Last fault number | Most recent trip; the value displayed in the operator panel. |
| r0947[1] | Acknowledged fault | Fault that has been cleared but remains in the buffer for diagnostic reference. |
| r0948[0] | Fault value for r0947[0] | Additional numeric information (counter, sub-code) for the most recent fault. |
| r0949[0] | Fault counter | Total number of fault events since last power-up or factory reset. |
| r0950 | Fault memory reset | Set to 1 to clear the entire fault history. |
When DriveMonitor shows the parameter list, the right-hand pane lists every fault buffer entry. Always record r0947[0] and r0947[1] before clearing, because the second entry often reveals the root cause (e.g., an older F0070 that is still being serviced by the PLC).
3. F0060 - ASIC Time Slice Overflow
F0060 is one of the most serious internal faults on MM420. It indicates that the Application Specific Integrated Circuit (ASIC) that handles internal time-sliced communication has overflowed. In practice this means the main processor missed a scheduled service window for a peripheral block (I/O, CB, encoder feedback, BOP link, etc.).
3.1 Documented Causes
- Internal firmware fault in the control board ASIC scheduling logic.
- Excessive interrupt load from a misbehaving Communications Board or feedback option.
- Power-supply ripple or brownout during the time slice window.
- Insertion/removal of option modules while the drive is energized (hot-swap on a non-hot-swap design).
3.2 Standard Siemens Diagnosis & Remedy
- Power the drive off completely (DC bus must discharge; wait until the LED on the BOP is dark).
- Remove all option modules and re-insert them one at a time after power-up.
- Re-apply power and observe whether F0060 re-appears within 60 seconds.
- If the fault recurs with no CB module attached, the control board is suspect and the inverter must be replaced or sent to a Siemens service center.
4. F0070 - CB Setpoint Fault (Telegram Failure)
F0070 is the fault that almost always appears first when the PC RS232 kit is used in place of a Profibus module. According to the MICROMASTER 420 parameter list (Function Manual, edition 01/2006, section 4.6), F0070 means:
"No setpoints received via the communications board during the telegram failure time (P2040)."
4.1 Cause Tree
- CB module physically removed, but drive still configured for CB setpoint (P0700, P1000).
- CB module present, but PLC is in stop or bus cable is broken.
- CB telegram failure time (P2040) is set to a value the network cannot meet (e.g., 0 ms when PZD cycle is 10 ms).
- Incorrect CB parameterization (P2041) for the installed module type.
- CB DIP-switch address conflicts with another node on the Profibus segment.
4.2 Why It Trips When Using the RS232 Kit
The PC RS232 kit connects to the drive's serial interface (X27 on the control board) and uses USS protocol at P2010 (baud), P2011 (USS address), P2012 (PZD), P2013 (PKW). However, the kit does not drive the CB slot. If the drive's control source is set to CB (P0700 = 6, P1000 = 6) and the CB is absent, the ASIC will time out the cyclic PZD exchange and raise F0070. The fact that DriveMonitor can read parameters does not change this, because USS is a polled, acyclic diagnostic channel that is independent of the cyclic CB channel.
5. Hardware Reference: PC RS232 Kit vs. Profibus CB
| Item | Order Number | Slot | Protocol | Function |
|---|---|---|---|---|
| PC RS232 connection kit | 6SE6400-1PC00-0AA0 | X27 / front serial | USS (PZD+PKW) | Parameterization with DriveMonitor / STARTER |
| Profibus CB module | 6SE6400-1PB00-0AA0 | CB slot (left side) | Profibus DP-V0/V1 | Cyclic setpoint + acyclic PKW |
| DeviceNet CB | 6SE6400-1DN00-0AA0 | CB slot | DeviceNet | Cyclic setpoint + explicit messaging |
| CANopen CB | 6SE6400-1CB00-0AA0 | CB slot | CANopen DS301 | Cyclic PDO + SDO |
The two interfaces are electrically and logically separate. You can keep the CB plugged in and route DriveMonitor through the front RS232 (USS) at the same time. That is the safest way to access the drive while keeping the PLC handshake alive.
6. Parameter Map for MM420 Communications
Before making any change, document current values. DriveMonitor supports uploading a parameter image (File > Upload Drive Image) and saving it as *.dn2. Always keep a copy offline.
| Parameter | Function | Typical Default | Notes for This Fault |
|---|---|---|---|
| P0700[0..2] | Selection of command source | 2 (terminal) | Must be set to a value the drive can actually receive (e.g., 2 or 1) when no CB is present. |
| P1000[0..2] | Selection of setpoint source | 2 (analog) | If P1000 = 6 (CB), F0070 will trip the moment P2040 elapses without a PZD. |
| P2010[0..1] | USS baud rate | 6 (9600) | Index 0 = COM link (front RS232), index 1 = BOP link. |
| P2011[0..1] | USS node address | 0 | Set to 1..31 for multi-drop; do not duplicate with P0918 (CB Profibus address). |
| P2012[0..1] | USS PZD length | 2 | Matches PZD word count expected by DriveMonitor / PLC. |
| P2013[0..1] | USS PKW length | 127 (variable) | 127 enables full PKW access in DriveMonitor. |
| P2014[0..1] | USS telegram off time | 0 (off) | If > 0, missing USS telegrams will fault the drive. |
| P0918 | CB Profibus address | 3 | Set via DIP switches on the CB itself. |
| P2040 | CB telegram failure time (ms) | 10 | Increase to a value at least 2x the Profibus cycle (typical 50-100 ms). |
| P2041[0..4] | CB parameterization | 0 | Index 0 = 0 (no special func); set per installed CB. |
| P2042 | CB PZD word count | 2 | Must match the PLC's configured PZD length. |
7. Step-by-Step: Connect DriveMonitor Without Tripping F0070
7.1 Prerequisites
- Drive is fully de-energized; the 10-minute DC-bus discharge time on MM420 has elapsed (or the BOP display is dark).
- RS232 cable is shielded; the PC end is a 9-pin D-sub; the drive end is the keyed mini-DIN supplied with the kit.
- DriveMonitor is installed at the firmware level appropriate to the drive (MM420 firmware V1.5 or V2.1 are the most common; DriveMonitor 5.x supports both).
7.2 Procedure
- Insert the PC RS232 kit cable into the X27 port on the bottom of the MM420 control board. Do not touch the CB slot.
- Connect the 9-pin D-sub to the engineering PC. If the PC has only USB, use a known-good USB-to-RS232 adapter (FTDI chipset is recommended); avoid unbranded CH340 clones on long cable runs.
- Launch DriveMonitor, select PC <-> Drive, choose Serial / USS, and configure the COM port to match P2010 (default 9600 baud, 8E1, no handshake).
- Click Online. DriveMonitor should now read r0947. If the drive trips immediately, record r0947 and r0948 before clearing the fault buffer.
- Change the control source so the drive does not require a CB PZD while you are working offline. The standard commisioning approach is:
- Set P0700[0..2] = 2 (terminal/digital inputs as command source).
- Set P1000[0..2] = 2 (analog input 1 as setpoint source).
- If you want to keep the PLC handshake alive for the rest of the machine, leave the Profibus CB plugged in and route DriveMonitor through the front RS232; the two channels coexist.
- Clear the fault buffer by setting r0950 = 1 (or by clicking Faults > Acknowledge All in DriveMonitor). Power-cycle the drive so the ASIC state is rebuilt from scratch.
8. Fault Acknowledgment Methods Compared
| Method | Action | Works Without CB? | Notes |
|---|---|---|---|
| DriveMonitor: Faults > Acknowledge All | Writes the acyclic PKW clear command | Yes (USS) | Requires the drive to be online and not actively faulted. |
| BOP: FN key combination | Press FN then arrow-up on BOP | Yes | Only clears latched faults if P0010 is at 0 and the run command is low. |
| Digital input | Configure one DI to P2103 or P2104 and pulse it | Yes | Most reliable for site work without a PC. |
| Power cycle | Remove line, wait for DC bus discharge, re-apply | Yes | Clears transient faults but does not erase the history buffer. |
| Factory reset | Set P0010 = 30, P0970 = 1 | Yes | Resets all parameters to defaults; back up the parameter image first. |
9. DIP-Switch and LED Reference for the Profibus CB
When the CB is present, verify the address and the bus health before the PLC is the suspect.
| Profibus CB LED | Color | Meaning |
|---|---|---|
| OFF (no LED) | None | No power or CB not seated. |
| Green, steady | Green | Data exchange (cyclic PZD) active. |
| Green, flashing | Green | DP-V1 acyclic channel active; no cyclic yet. |
| Red, steady | Red | Watchdog expired; PLC is in stop or bus broken. |
| Red, flashing | Red | Parametrization error (P2041, P0918 mismatch). |
The Profibus node address is set by DIP switches S1..S7 on the CB (binary weighting 1, 2, 4, 8, 16, 32, 64). S8 selects hardware addressing. After changing switches, you must power-cycle the drive (or send a Profibus "Set Slave Address" service) for P0918 to update.
10. Verification Checklist
- With the RS232 kit online, read r0947[0] and r0947[1] - both should now read 0 (or "No fault").
- Read r0949; it should be 0 after the power cycle that followed the acknowledgment.
- Confirm P0700 and P1000 reflect the intended control source for the offline diagnostic state.
- If the Profibus CB is the project's final interface, reconnect it, set the bus master to "Operate", and verify the CB LED goes solid green within P2040 ms.
- Issue a 0 Hz / 0 V setpoint over Profibus and run the motor briefly with the BOP in HAND mode; this confirms analog and digital inputs still work after the parameter changes.
11. Extended Diagnostics and Edge Cases
11.1 F0060 Recurs After F0070 Is Cleared
Perform a factory reset (P0010 = 30, P0970 = 1). If F0060 still trips within 5 s of power-up, the control board's ASIC scheduler is defective. This is hardware. Replace the drive or the control board (CUSA-XXX-XXX depending on frame size).
11.2 F0070 Trips Even With CB Installed and PLC Cycling
- Inspect the bus connector and the terminating resistor (must be ON at both physical ends, OFF in between).
- Confirm the PLC's configured PZD length matches P2042.
- Check that the GSD file is the correct one for firmware V1.5 / V2.1 (Siemens Drive ES GSD, file name SIEM808F.GSD for the V2 generation).
11.3 RS232 Link Drops Randomly Under Electrical Noise
The X27 port is on the same control board as the I/O; routing the cable parallel to a VFD output cable will corrupt the 24 V housekeeping and the USS frames. Keep a minimum 200 mm separation and cross at 90 degrees if intersection is unavoidable.
11.4 Using the AOP (Advanced Operator Panel) for Diagnostics
When DriveMonitor or a PLC is not available, the AOP can be parked on the drive to read r0947 in plain text. The AOP also shows the parameter index that contains the fault value, which is helpful when multiple faults are latched. The BOP will only show the first numeric code; the AOP shows the full text description.
12. Frequently Asked Questions
Why does DriveMonitor show parameters correctly while F0070 stays latched?
DriveMonitor communicates through the front X27 RS232 port using USS, which is acyclic and polled. F0070 monitors the cyclic PZD exchange on the CB slot. The two channels are independent, so reading parameters does not satisfy the cyclic-setpoint watchdog.
Do I have to remove the Profibus module to use the PC RS232 kit?
No. Keep the Profibus CB plugged in. The PC RS232 kit connects to the front serial port (X27) and can run at the same time as the fieldbus. This avoids F0070 because the CB telegrams continue normally.
What value of P2040 is appropriate for a Profibus network with a 10 ms bus cycle?
Set P2040 to at least 2x the bus cycle, typically 50-100 ms. The value must be longer than the longest expected PLC stop or bus interruption; otherwise the drive will trip on every PLC restart.
After acknowledging F0070, the fault returns on the next power-up. Why?
Because the drive's command source is still configured to CB (P0700 = 6 or P1000 = 6) and the telegrams are not arriving. Acknowledging the fault clears the latch but does not change the source selection; the next time the watchdog expires the fault is raised again.
Is F0060 always a hardware failure?
On the MM420, F0060 is the ASIC time-slice overflow and the manual directs the user to replace the inverter or contact customer service. However, when it appears together with F0070, it is often a secondary trip caused by the CB-comms interruption and can be cleared by resolving F0070. If F0060 appears on a stand-alone drive with no CB and no option modules, treat it as a hardware failure.