Overview
Engineers integrating a legacy Siemens MICROMASTER 420 (MM420) drive into a SIMATIC S7-300 automation cell frequently need to parameterize the drive from a PC without running a second serial/USB cable directly to the inverter. The supported method is to install STARTER commissioning software on the engineering station, let it ride on top of STEP 7 routing, and tunnel the parameterization protocol through the S7-300 PROFIBUS master into the MM420 PROFIBUS slave.
This reference describes the complete routed configuration:
- Engineering PC → MPI/PROFIBUS/Ethernet → S7-300 CPU
- S7-300 PROFIBUS DP master → MM420 with PROFIBUS option module
It assumes STEP 7 V5.5 + Service Pack x for HW Config, the Drive ES Basic / STARTER commissioning toolchain compatible with MM420, and an MM420 fitted with the 6SE6400-1PB00-0AA0 PROFIBUS option. The drive is treated as a DP-V0 slave, not an isochronous peer, since MM420 predates PROFIdrive profile V4.
System Architecture and Prerequisites
The routed topology replaces a direct USB-to-MMI link with a three-segment path. The PC only sees the S7-300 station; the S7-300 forwards the PG/PC request across its PROFIBUS DP subnet to the MM420 using the S7 routing service.
Prerequisites checklist
- STEP 7 V5.5 (SPx) installed, including NetPro and HW Config. TIA Portal V16 and later does not support MM420; do not attempt to import the project there.
- STARTER commissioning software installed with the MICROMASTER 420 device library. Confirm via Help → About; the version range typically goes up to STARTER V5.4 for MM420. Newer SINAMICS STARTER distributions are listed in entry 26233208.
- MM420 GSD file installed in STEP 7 (Siemens part number 6SE6400-1PB00-0AA0 ships with a CD containing SIEM080D.GSD or its revision).
- MM420 PROFIBUS option module 6SE6400-1PB00-0AA0 seated in the drive's option slot; otherwise the drive has no PROFIBUS interface at all.
- PG/PC cable: PC Adapter USB (MPI/PROFIBUS) for 1.5 Mbps, or Ethernet to a CP343-1 Lean / CP343-1 Advanced on the S7-300 for higher throughput.
Hardware Installation: MM420 PROFIBUS Module
The MM420 base unit exposes a removable cover plate on the lower front. The PROFIBUS option module is inserted from below, latches into the option slot, and exposes a 9-pin sub-D female (PROFIBUS DP) on the bottom of the drive. Termination is set on the module with the two slide switches:
| Switch | OFF | ON | Rule |
|---|---|---|---|
| Term. (left) | Bus not terminated | Termination ON (220 Ω between A/B, +5 V on cable shield) | ON only on the physical end node of the segment |
| Term. (right) | Bus not terminated | Termination ON (same as above, redundant contact) | ON only on the physical end node of the segment |
Pin-out on the sub-D is the standard PROFIBUS DP assignment (pin 3 RxD/TxD-P, pin 8 RxD/TxD-N, pin 6 +5 V, pin 5 GND, pin 4 RTS). Shield continuity must be maintained with 360° clamp-on backshells; do not rely on the D-sub shell alone for EMC compliance.
After mechanical install, the drive must be told that PROFIBUS is the command and setpoint source. Either program these from the BOP (Basic Operator Panel) before commissioning, or push them later through the STARTER routed session:
| Parameter | Value | Meaning |
|---|---|---|
| P0700 | 6 | Command source = PROFIBUS |
| P1000 | 6 | Setpoint source = PROFIBUS |
| P0918 | 3 (default) | PROFIBUS slave address; must be unique on segment |
| P0927 | 15 | Permits parameter modification from PROFIBUS (PKW) |
| P2051.0 | 52 | PZD1 = control word 1 (STW1) |
| P2051.1 | 21 | PZD2 = main setpoint (NSOLL_A) |
| P2051.2 | 53 | PZD3 = status word 1 (ZSW1) |
| P2051.3 | 20 | PZD4 = actual frequency (NIST_A) |
If the BOP is not available, set P0918 first via the PC <> drive direct cable (BOP-link, part 6SE6400-1PC00-0AA0) before going through the routed path. STARTER can change these once the routed session is up.
STEP 7 Hardware Configuration with GSD
Open the S7 project in STEP 7 Manager and launch HW Config. The S7-300 station must already contain the CPU (e.g. 6ES7315-2EH14) with PROFIBUS DP master enabled, plus the CP/interface that the PG will use to reach the CPU.
- Install the GSD. Options → Install GSD File. Browse to the SIEM080D.GSD (or its revision) provided with the PROFIBUS module. STEP 7 compiles it into the hardware catalog under PROFIBUS DP → Drives → Siemens AG → MICROMASTER 4.
- Add the MM420 to the DP master system. Drag the MM420 from the catalog onto the DP master system line. STEP 7 prompts for a PROFIBUS address — enter the same value as P0918 (default 3).
- Select a PPO type. The dialog box lists PPO 1, 2, 3, 4, 5. For parameterization through the PKW channel, choose PPO 1 (4 PKW + 2 PZD) if you only need control and minimal status, or PPO 5 (4 PKW + 10 PZD) for full access. Avoid PPO 3 and PPO 4 because they omit the PKW area; STARTER cannot read or write parameters without PKW.
- Map I/Q addresses. STEP 7 assigns the PZD area into the process image. Typical mapping: input/output words 256..267 for PPO 5. The PKW area is not bound to the process image; STARTER uses it through acyclic S7 functions.
- Save, compile, and download HW Config to the CPU. Without a download, the master will not poll the MM420, and STARTER will not see the slave.
PG/PC Interface Configuration for S7 Routing
The S7 routing function is a property of the PG/PC interface. If the access point is set to TCP/IP → Network card with no routing table, STARTER will only see the directly attached subnet. Switch the interface to the S7 routing-capable access point.
- Open Start → Control Panel → Set PG/PC Interface.
- Select the access point S7ONLINE (STEP 7) → PC Adapter (MPI) / PC Adapter (PROFIBUS) / TCP/IP → <your network card>. The choice depends on the physical cable from PC to S7-300.
- Click Properties and confirm the baud rate (MPI: 187.5 kbps or 1.5 Mbps; PROFIBUS: 1.5 Mbps or 12 Mbps; Ethernet: auto-negotiate).
- Close with OK. The interface is now enabled for S7 routing.
To verify routing before launching STARTER, open SIMATIC Manager → Accessible Nodes. The CPU should appear. Double-click it: SIMATIC Manager runs a routing diagnostic and reports the bus topology. If the MM420 does not appear yet, that is normal at this stage — STARTER will resolve it through the configured DP slave.
STARTER Project Configuration
Create a new STARTER project that mirrors the S7-300 station, then add the MM420 as a PROFIBUS child of the PLC. STARTER is offline-aware: project work, parameter editing, and online connection are separate states.
- Launch STARTER. Project → New. Give the project a name and a storage path that is also reachable by STEP 7 (recommended: keep the project in the same directory tree).
- Insert → SIMATIC S7-300 station. The icon appears in the project tree.
- Right-click PROFIBUS on the S7-300 station → Insert drive → choose MICROMASTER 4. If the device is not in the list, the STARTER install does not contain the MM420 device pack. Re-run the setup and add the legacy components, or fetch the latest bundle from entry 26233208.
- Match the PROFIBUS address (default 3) and PPO type (1 or 5) to the STEP 7 HW Config entry. Mismatches cause the slave to time out on parameter access.
- Double-click the MM420 to open the parameter list. Adjust P0700, P1000, P0927, P0918 as required. Save the project before going online.
Establishing the Routed Online Connection
With the PC interface on S7ONLINE and the S7-300 reachable, STARTER can tunnel through the CPU into the MM420. The handshake uses the S7 routing protocol: a PG function issued to the CPU is forwarded across its DP master to the slave.
- In STARTER, right-click the MM420 → Connect to target system. The dialog shows the routing path PC → [S7ONLINE interface] → S7-300 → PROFIBUS → MM420.
- If the dialog prompts for the access point, choose S7ONLINE (STEP 7) (not the older DEVICE point used for direct RS232 access).
- STARTER issues a parameter request. The CPU's DP master forwards the read/write to the MM420 using PKW. The first connection usually takes 3–5 seconds while PKW negotiates with the slave.
- When online, the parameter list shows the current drive values. The status bar at the bottom of STARTER shows Online: routed via S7-300.
- Use the RAM to ROM button (the disk icon) to commit changes to the MM420's non-volatile memory once you have finished parameter editing. Without this step, the drive reverts to the old values after power off.
To bring the drive to RUN through the same routed path, write the standard PROFIdrive control word 0x047E (unblock + setpoint enable + ramp enable) into PZD1, and a normalized setpoint (0x4000 = 100 %) into PZD2. The control word is mapped in the S7 process image at the addresses STEP 7 assigned in HW Config. Use a watch table in STEP 7 or a small FB that does an SFC 58 / SFC 59 WR_REC / RD_REC call to push PZD into the slot — this is the cleanest way to exercise control while STARTER is still online for monitoring.
Parameter Access and Operations
STARTER exposes the full MM420 parameter set (P0003 selects access level, P0004 hides filters). The routed session is functionally identical to a direct USB link, with one limitation: bulk parameter downloads (writing the entire parameter set with one button click) are slower because every parameter goes through the S7 routing service. Plan for roughly 200–400 ms per parameter at 1.5 Mbps DP baud.
| Operation | Mechanism | Typical cycle |
|---|---|---|
| Read single parameter (Pxxxx) | PKW read request, ID 1 | 30–80 ms |
| Write single parameter | PKW write request, ID 2 | 50–120 ms |
| Read indexed parameter (e.g. P2051) | PKW read with sub-index | 50–100 ms |
| Read fault buffer (r0947) | PKW read of indexed parameter | 60–120 ms |
| Save to MM420 EEPROM (P0971 = 1) | PKW write triggers RAM→ROM copy | 2–8 s depending on size |
| Drive control via PZD | Cyclic PZD, independent of STARTER | Bus cycle, e.g. 5 ms |
To script parameter access, use STARTER's Scripting interface (VBScript) or drive a DDE link from STEP 7. Both methods travel the same routing path. For non-Windows tooling, use the SFC 58/59 acyclic record read/write on the DP slave diagnostic slot; STARTER can be kept as the visualization layer.
Verification, Diagnostics, and Troubleshooting
After every parameter change, validate that the drive has accepted the new value. STARTER highlights the parameter in green when the online value matches the offline value; red means a write is pending or failed. For a non-STARTER sanity check, switch the MM420 to the BOP and read the parameter directly.
| Symptom | Root cause | Remediation |
|---|---|---|
| STARTER shows Slave not found | PROFIBUS address mismatch between STARTER project and STEP 7 HW Config; or P0918 set differently on the drive | Compare all three. Re-flash P0918 from the BOP if needed |
| PKW errors during parameter read | PPO 3 or PPO 4 selected (no PKW area) | Change HW Config to PPO 1 or PPO 5; reload CPU |
| Drive faults F0070 / F0071 | PROFIBUS link dropped or watchdog timeout | Check connector pinout, baud rate, termination; check P0927 |
| STARTER hangs at Connecting... | PG/PC interface set to TCP/IP auto, no S7 routing enabled | Switch Set PG/PC Interface to S7ONLINE with the right hardware |
| Online OK but parameters are read-only | P0927 <> 15 (PROFIBUS parameter modification disabled) | Set P0927 = 15 via BOP or via the parameter list directly |
| Drive responds to STARTER, but PLC loses cyclic I/O | Address overlap — PZD area collides with another module | Re-assign the MM420 slot to free I/Q range in HW Config |
| Values revert after power off | RAM→ROM not executed | Click the RAM→ROM button in STARTER, or write P0971 = 1 |
| Routing OK in STEP 7 but STARTER times out | STARTER version newer than V5.4; MM420 library removed | Reinstall an older STARTER or fetch the legacy device pack from entry 26233208 |
For deeper diagnostics, open the MM420 Faults & Warnings tab in STARTER. The most common routed-deployment faults are F0070 (PROFIBUS comm loss), F0071 (watchdog), and F0080 (PROFIBUS initialization error). Each one is a latched bit in r0947; clearing requires a positive-edge on the PROFIdrive control word bit 7, or a power cycle if P0947 is not zero.
Which PPO type should I select for parameterization through STARTER?
Use PPO 1 (4 PKW + 2 PZD) for simple control loops with occasional parameter reads, or PPO 5 (4 PKW + 10 PZD) if you need full status words. PPO 3 and PPO 4 omit the PKW area, so STARTER cannot read or write MM420 parameters through them.
Can I keep the project in TIA Portal and still route STARTER to the MM420?
No. TIA Portal V16 and later have no MICROMASTER 4 catalog entry. Keep the S7-300 project in STEP 7 V5.5 and run STARTER separately. STARTER can read the S7 routing table from STEP 7, so you do not need to re-enter the topology.
Why does STARTER see the CPU but not the MM420?
Three usual reasons: the PROFIBUS address in STARTER does not match P0918, the PPO type in STARTER differs from HW Config, or the option module 6SE6400-1PB00-0AA0 is not seated and powered. Check the address and PPO first, then re-seat the module.
Do I need a CP343-1 to route STARTER to MM420?
Not necessarily. Routing works over MPI (PC Adapter USB at 187.5 kbps or 1.5 Mbps) as well as Ethernet through a CP343-1 Lean or CP343-1 Advanced. Ethernet is preferred for larger projects because routing latency scales with PG traffic.
How do I commit parameter changes permanently to the MM420?
Click the RAM→ROM button in STARTER, or write the value 1 to parameter P0971 through the PKW channel. Without this step, the MM420 reverts to the previous values on the next power off.
Where can I confirm the latest STARTER version that still supports MM420?
Check the SINAMICS STARTER overview on the Siemens Industry Online Support portal, entry 26233208. The page lists the three most recent STARTER versions and their service packs, plus the links to the support packages that bundle the MICROMASTER device library.