Resolving F0070 on Siemens MM420 PROFIBUS: Migration Guide

Problem Overview: F0070 After MICROMASTER Vector to MM420 PROFIBUS Migration

Replacing a damaged Siemens MICROMASTER Vector drive (catalog 6SE3290-0XX87-8PB0 module) with a MICROMASTER 420 (MM420) on an existing SIMATIC S7-316-2DP PROFIBUS network is a common retrofit scenario in brownfield plants. The replacement unit communicates through a PROFIBUS option board catalog 6SE6400-1PB00-0AA0. After commissioning the new drive, the most frequent failure mode is a hard F0070 fault that prevents the MM420 from being controlled by the PLC, even though the PROFIBUS LED on the option board may report a green, healthy bus link.

The fault cascades in two phases:

1. Initial F0070 trip on every start attempt, caused by telegram monitoring timeout (parameter P2040 too aggressive versus the STEP 7 PROFIBUS OB cycle).
2. Once P2040 is relaxed, F0070 clears but the drive still does not run. The PLC diagnostic buffer flags an I/O access error at PEB/PAB address 256, and the drive's r0052 status word shows bit 0 (Drive ready) toggling while r0054 control word never asserts bit 0 (ON/OFF1).

This article resolves both phases with a complete parameter, control-word, and hardware configuration reference, including the migration deltas between MICROMASTER Vector (MM V) and MM420 control interfaces.

F0070 Fault Code Technical Definition

F0070 on MM420, MM430, MM440, and SINAMICS G120 (CU240x-DP) means Communication Board (CB) telegram failure. The internal CB watchdog, configured by P2040, expires because the expected cyclic PZD telegram was not refreshed within the configured interval. The drive responds by coast-stop (OFF2) and latches F0070. A fault acknowledge (rising edge on control word bit 7, or digital input on P2103...P2106) is required to clear the latch.

Additional related faults on the same family include F0071 (USS/Modbus link failure on COM link) and F0072 (SLT/USS timeout on the OP/USS interface). On a PROFIBUS migration, F0070 is the dominant signature.

Root Cause: PROFIBUS Communication Board (CB) Configuration

Five contributing causes must be cleared in sequence before the drive will accept a start command from the PLC:

1. P2040 set below PROFIBUS cycle time. The default P2040 = 20 ms is below the typical STEP 7 DP cycle (often 50–100 ms) when the bus runs at 1.5 Mbit/s and contains multiple slaves. The CB watchdog trips on the first minor bus jitter.
2. Mismatch between the new MM420 GSD file and the existing HW Config slot. The MM V (6SE3290-0XX87-8PB0) and MM420 (6SE6400-1PB00-0AA0) use different GSD/GSX files. Continuing to use the old GSD after hardware swap leaves the slot in module error state; the PLC raises I/O access fault at PEB/PAB 256.
3. DIP switch versus P918 priority. On 6SE6400-1PB00-0AA0, the rotary/DIP switches define the slave address, and P918 is read-only when the switches are non-zero. With all DIPs OFF, the PROFIBUS address is taken from P918 only. Mismatch between HMI/STARTER value and the HW Config slave address will cause the PLC to communicate with a non-existent device and trigger I/O access errors.
4. Wrong PPO type selected. MM V can be configured for PPO1 (4 PKW + 2 PZD) or PPO3 (0 PKW + 2 PZD). The MM420 default mapping expects PPO1. Selecting PPO3 in HW Config breaks the assumed PKW channel offset and corrupts PZD decode.
5. Command source (P0700) and setpoint source (P1000) not set to CB. The MM420 ships with command source set to terminal default (P0700 = 2). The PROFIBUS CW1 cannot start the drive until P0700 = 6 (CB on COM link) and P1000 = 6 (CB setpoint) are active.

Prerequisites Before Parameter Configuration

• Starter / DriveMonitor (or STARTER V5.x) installed on engineering PC and online with the MM420 via RS485 or PROFIBUS.
• STEP 7 V5.5 (or TIA Portal with GSD import) project containing the new MM420 GSD file SIEM8044.GSD for MM420 PPO1.
• PLC in STOP, with the program consistency check pre-validated against the new HW Config.
• DIP switches on the 6SE6400-1PB00-0AA0 module physically set to OFF (0) so P918 is the active address source.
• Bus termination verified (resistor ON at both physical ends only).

Step-by-Step Parameter Configuration

Apply the following values using Starter/DriveMonitor. After each change, the drive must be saved via P0971 = 1 for volatile parameters, or a full P0010 = 30, P0970 = 1 factory reset followed by a re-commissioning if migrating from a project that contained an MM V.

1. Set the PROFIBUS slave address: P0918 = 10 (matches the STEP 7 HW Config slot 10).
2. Set the CB telegram monitoring time: P2040 = 1000 ms (1 s). Recommended range for non-safety PP1 cycles: 500–2000 ms. Do not exceed 5000 ms; safety-related monitoring requires a separate SIL path.
3. Set command source to PROFIBUS CB: P0700 = 6 (CB on COM link).
4. Set setpoint source to PROFIBUS CB: P1000 = 6.
5. Select the PPO type on the CB (legacy MM4): P2041 = 0 for PPO1 (4 PKW + 2 PZD), or P2041 = 1 for PPO3 (0 PKW + 2 PZD). Use PPO1 unless the existing PLC program exclusively uses process data and never reads parameters.
6. Configure BICO command routing (P840–P852) per the table below.
7. Set ramp times: P1120 = 10 s (ramp-up), P1121 = 10 s (ramp-down) for a conservative first run.
8. Set motor data: P0304 (rated voltage), P0305 (rated current), P0307 (rated power), P0310 (rated frequency), P0311 (rated speed). Perform auto-tune: P1910 = 1, then issue an OFF1/ON1 cycle.
9. Save: P0971 = 1.

PROFIdrive Control Word and Status Word Decoding

MM420 implements the PROFIdrive Standard Telegram 1 (formerly PPO1) on the first two PZD words of the PZD2 channel:

STW1 (Control Word 1) — Bits per PROFIdrive Profile 1

For a forward run, the PLC must issue the two-step sequence described in the MICROMASTER PROFIBUS optional board manual:

1. Send STW1 = 0x047E (binary 0000 0100 0111 1110) — bits 1–6 set, bit 0 = 0. This transitions the drive from Switching On Inhibited to Ready For Switch On.
2. Send STW1 = 0x047F (binary 0000 0100 0111 1111) — bit 0 transitions 0→1, which the drive interprets as the rising edge required to enter Operation Enabled.

For forward run at 12.5 Hz (setpoint scaling 0x4000 = 50 Hz), send PZD2 = 0x1000; for 50 Hz, send PZD2 = 0x4000. The full PZD2 frame for a 12.5 Hz forward run is therefore 0x047F 0x1000 (PZD1 first, PZD2 second on the wire, little-endian per word). The standard "run at nominal" frame is 0x047F 0x4000.

ZSW1 (Status Word 1) — Bits per PROFIdrive Profile 1

The status value reported in the source — r0052 = 111110100011001 (binary, read LSB right) — decodes as:

• Bit 0 = 1 (Ready to switch on)
• Bit 3 = 0 (No active fault — F0070 cleared)
• Bit 6 = 0 (Switch-on inhibit cleared)
• Bit 14 = 1 (Motor rotation direction detected)

Combined with the control word r0054 = 0100010001111110, bit 0 = 0 (OFF1 asserted). The PLC is sending 0x044E rather than the required 0x047E/0x047F sequence, so the drive accepts only the OFF2/OFF3=OK, Enable Operation, Enable Ramp, Unfreeze, Enable Setpoint pattern, but never receives the ON command. This is the second-phase symptom — F0070 is gone, but the drive stays in Ready For Switch On state and never transitions to Operation Enabled.

BICO Parameter Mapping: P840 to P852

With P0700 = 6 and P1000 = 6, the MM420 routes PROFIBUS STW1 bits to digital control functions via the BICO parameter set P840…P852. The default values are already PROFIdrive-correct on a stock MM420 firmware ≥ 1.31, but a migration reset wipes them. Validate each one.

S7-316-2DP Hardware Configuration with GSD File

Use STEP 7 HW Config to install the MM420 GSD file SIEM8044.GSD and configure slot 10 (or whichever PROFIBUS address matches P0918). The slot occupies a PPO1 image: 4 PKW words (input + output, address offset 0–7) and 2 PZD words (input + output, address offset 8–11). Confirm the I/O start addresses in the slot properties:

The PLC diagnostic "I/O access error 256" reported in the user's buffer indicates the slot exists in HW Config at the right address, but a PKW read (SFC 59 / SFB 53) is targeting the PZD range — the PKW channel was skipped. The fix is to address PZD explicitly at PEB 264 (ZSW1) and PEB 266 (NIST) on the receive side, and to write PAB 264 (STW1) and PAB 266 (NSOLL) on the send side. The L/T access to PKW requires a DPVO read/write (DPRD/DDWR / DPWR_DAT) on bytes 256–263.

After GSD install, recompile HW Config, download to the CPU, and STOP→RUN the CPU. The OB82 (I/O fault) diagnostic must clear before any subsequent test.

Diagnostics: Reading r2050 and Identifying Telegram Errors

The r2050 values reported in the source — r2050[0] = 17534 and r2050[1] = 8304 — are the most recently received PZD1 and PZD2 words. Decoded:

Note that 0x2070 for NSOLL is non-standard; typical frames use 0x4000 (100 %) or 0x1000 (25 %). The odd value suggests a derivative HMI/SCADA tag with unit conversion (0x2070 = 8304 in raw counts, possibly a frequency * 16 representation). Confirm the scaling of P2000 (reference frequency) when comparing raw NSOLL to engineering units. The PZD2 issue is secondary; correcting STW1 bit 0 alone will allow the drive to ramp to whatever NSOLL is currently held.

Verification Procedure

1. Connect Starter / DriveMonitor online. Confirm P0010 = 0 and r0002 = 0 (drive status: drive running = 0; fault = 0; mains on = 1).
2. Read r0052 in Starter; bit 0 (Ready to switch on) must be 1 and bit 3 (Fault) must be 0.
3. From a STEP 7 VAT, write a single PZD2 frame to PAB 264: STW1 = 0x047E, NSOLL = 0x0000. Wait 100 ms. Read PEB 264. ZSW1 should be 0x0431 (Ready to switch on, Ready to operate, Switch-on inhibit).
4. Write the second frame: STW1 = 0x047F, NSOLL = 0x0000. ZSW1 should transition to 0x0233 (Operation enabled, no fault). Setpoint of 0x0000 → 0 Hz.
5. Write a third frame: STW1 = 0x047F, NSOLL = 0x1000 (12.5 Hz on 50 Hz motor). Confirm motor accelerates to ~12.5 Hz within P1120 seconds; r0021 matches r0020 within P2165 tolerance.
6. Issue OFF1: STW1 = 0x047E, motor ramps down per P1121. Issue OFF2: STW1 = 0x043E (bit 1 = 0). Motor coasts. Issue OFF3: STW1 = 0x047A (bit 2 = 0). Motor quick-stops per P1135.
7. Force a fault by disabling P2040 = 5 ms and stopping the PLC for 1 second. Drive should latch F0070; acknowledge with STW1 bit 7 rising edge.
8. Restore P2040 = 1000 ms and P0971 = 1.

Migration Pitfalls: MICROMASTER Vector to MM420 Differences

The MICROMASTER Vector (6SE32 series) and MM420 share the MM4 control platform but differ in several ways relevant to a brownfield swap:

If the application relied on sensorless vector closed-loop performance, an MM420 will not match the MM Vector's dynamic response. For a true drop-in upgrade, consider the SINAMICS V20 (basic V/f) or G120C (with vector control via CU240E-2) as a replacement rather than the MM420, which is now an end-of-life, service-only product on the Siemens portfolio.

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Frequently Asked Questions