CM 1242-5 PROFIBUS DP Slave to ProSoft MVI56-PDPMV1 Master: Configuration Reference

Overview

This reference describes the engineering required to bring a Siemens S7-1200 with a CM 1242-5 communications module online as a PROFIBUS DP slave behind a ProSoft MVI56-PDPMV1 PROFIBUS DP-V1 master installed in a ControlLogix chassis. The two devices sit on different vendor platforms, so the integration spans three independent engineering tools: TIA Portal (Siemens) for the slave side, ProSoft Studio (ProSoft Technology) for the master and PROFIBUS segment side, and Studio 5000 Logix Designer (Rockwell Automation) for the backplane data mapping on the ControlLogix side. The single most common stumbling block on this integration is the confusion between EDS and GSD files. The EDS is for EtherNet/IP and is consumed by Studio 5000; the GSD is for PROFIBUS and is consumed by the DP master. They are not interchangeable and they are not imported by the same tool.

The CM 1242-5 (Siemens article 6GK7 242-5DX30-0XE0) is a PROFIBUS DP-V0 slave only. The MVI56-PDPMV1 is a PROFIBUS DP-V1 class 1 and class 2 master. The engineering flow is therefore one-directional: only the master side requires a GSD file describing the slave, and only the master consumes it. The CM 1242-5 does not import anything about the MVI56-PDPMV1; a slave never consumes the GSD of a master, because slaves respond to a master's poll and do not build their own poll list.

Companion documentation in this area: the ProSoft Technology Knowledge Base article ProSoft KB 367 walks through a working S7-300 to MVI56-PDPMV1 setup and is directly transferable to a CM 1242-5 slave because the GSD-based import mechanism in ProSoft Studio is identical between the two Siemens slave families. The CM 1242-5 GSD itself is hosted on the Siemens Industry Online Support portal at Siemens Support entry 49852283, and the MVI56-PDPMV1 user manual is available from the MVI56-PDPMV1 product page under the Downloads tab.

Prerequisites

• Siemens S7-1200 CPU with firmware V4.0 or later. The CM 1242-5 hardware catalog entry appears in TIA Portal V14 SP1 and later; earlier TIA Portal versions will not see the module.
• Siemens CM 1242-5 communications module, article 6GK7 242-5DX30-0XE0, inserted on the left side of the S7-1200 CPU (slot 101 of the S7-1200 station).
• ProSoft MVI56-PDPMV1 single-slot ControlLogix form-factor module, installed in any local slot of the 1756 chassis. A 1756 backplane with adequate slot count and a 1756 power supply sized for the chassis population.
• ControlLogix processor such as 1756-L71, 1756-L72, 1756-L73, 1756-L81E, 1756-L82E, or 1756-L83E, running Studio 5000 Logix Designer V30 or later. CompactLogix 5380 (5069-L3x) is also supported by the MVI56-PDPMV1 in remote chassis over EtherNet/IP, but the MVI56 module itself must reside in a 1756 chassis.
• PROFIBUS DP cable (violet, type A, FC, shielded twisted pair with characteristic impedance 150 ohm) terminated with PROFIBUS D-sub connectors. Active or passive bus terminators at both ends of the segment.
• Engineering software: TIA Portal V14 SP1 or later (V15, V16, V17, V18, or V19 supported), ProSoft Studio (the current ProSoft configuration tool) and Studio 5000 Logix Designer V30 or later. A copy of RSLinx Classic is required only for the EDS install step.
• PROFIBUS segment design respecting the 32-station limit per segment, the single-baud-per-segment rule, and the segment-length versus baud-rate table. Refer to the PROFIBUS Installation Guide for the official type A cable lengths at each baud.

Hardware Identification and Order Numbers

Architecture and Data Flow

The integration has three logical layers. At the top, the Logix processor exchanges data with the MVI56-PDPMV1 over the ControlLogix backplane using a ProSoft-supplied Add-On Instruction. In the middle, the MVI56-PDPMV1 runs the PROFIBUS DP-V1 master and polls the CM 1242-5 over a violet PROFIBUS cable. At the bottom, the CM 1242-5 exchanges the cyclic I/O with the S7-1200 CPU over the internal backplane of the S7-1200 station, exposing the data as inputs and outputs that the S7-1200 user program reads and writes.

Every byte that travels from Logix to the S7-1200 user program crosses three boundaries: the Logix backplane to the MVI56-PDPMV1, the PROFIBUS segment between the MVI56-PDPMV1 and the CM 1242-5, and the S7-1200 internal backplane between the CM 1242-5 and the S7-1200 CPU. Each boundary can fail independently, which is why the verification steps in the commissioning section target each boundary separately.

GSD vs EDS - Why the MVI56-PDPMV1 Has Only an EDS

The first engineering question most integrators raise is "where is the MVI56-PDPMV1 GSD file?" The answer is that the MVI56-PDPMV1 is a master on the PROFIBUS segment, not a slave, so it has no GSD. A GSD (General Station Description) is a vendor-supplied ASCII text file (with the .GSD extension) that describes a DP slave to any DP master: vendor name, slave family, supported baud rates, I/O slot structure, diagnostic message structure, and timing parameters. The MVI56-PDPMV1, as a master, has nothing to describe about itself to another master.

The EDS file shipped from the ProSoft Technology downloads tab is the Electronic Data Sheet for EtherNet/IP (CIP) consumption by Studio 5000 / RSLinx. It registers the MVI56-PDPMV1 on the EtherNet/IP side (the side that faces the ControlLogix backplane and the Add-On Instruction that exchanges backplane data with the module). The EDS has no relevance to the PROFIBUS segment configuration and is not importable into TIA Portal as a PROFIBUS device description.

What is required for PROFIBUS is the GSD of the CM 1242-5. That GSD is published on the Siemens Industry Online Support site at Siemens Support entry 49852283, which contains the DP-V0 GSD for the CM 1242-5, the associated bitmap, and the related type / symbol files. Download the GSD (typically named SIEM812F.GSD or similar; confirm by reading the readme inside the ZIP), the BMP bitmap, and the type files (if any) into a single folder before importing.

Step 1 - Install the CM 1242-5 GSD in the ProSoft Master Configuration

1. Open ProSoft Studio and connect to the MVI56-PDPMV1 over the configuration Ethernet port (the front Ethernet port on the MVI56-PDPMV1, IP default 192.168.0.250 / 255.255.255.0) or via USB depending on the module's front-panel connectors.
2. Open the PROFIBUS Master configuration view. In current ProSoft Studio releases this is reached via the navigation tree under PROFIBUS > Master Settings.
3. Click "Import GSD" or "Add slave" and browse to the folder containing the CM 1242-5 GSD downloaded from the Siemens support page. ProSoft Studio accepts the standard PROFIBUS GSD file (SIxxxxxxx.GSD) and the associated bitmap file in the same folder.
4. After import, the CM 1242-5 appears in the master's slave catalog with the modules and I/O lengths the Siemens GSD declares. The GSD typically offers several modular slot choices (for example 4, 8, 16, or 32 words in each direction); select the modular width that matches the project requirement.
5. Assign a PROFIBUS node address to the CM 1242-5 in the master project. Valid addresses are 1 to 125, with 0 and 126/127 reserved by PROFIBUS convention (126 is often used for "no station" by some tools and 127 is the broadcast address).
6. Configure the cyclic I/O modules. Typical first integration starts with 4 words in each direction as a smoke test, expanding to 8, 16, or 32 words once the basic exchange is healthy. The combined cyclic I/O per slave is limited to 244 bytes IN and 244 bytes OUT (from the master's viewpoint) by DP-V0.
7. Set the segment baud rate. The MVI56-PDPMV1 auto-detects up to 12 Mbps; align this to the slowest slave on the segment because PROFIBUS runs at a single baud rate per segment. A 1.5 Mbps baud is a common conservative choice for mixed-vendor cells.
8. Save the project and download the configuration to the MVI56-PDPMV1 through ProSoft Studio. The MVI56-PDPMV1 stores the configuration in non-volatile memory and boots from that image on power-up.

For the exact menu paths, the ProSoft MVI56-PDPMV1 user manual is available on the MVI56-PDPMV1 product page under the Downloads tab. The companion KB article at ProSoft KB 367 shows a working S7-300 configuration screen-by-screen; the GSD-based import mechanism is identical to the CM 1242-5 path.

Step 2 - Configure the CM 1242-5 in TIA Portal

1. Open the S7-1200 project in TIA Portal and open Devices & Networks.
2. Add the CM 1242-5 in the device configuration of the S7-1200 station. The module sits in slot 101 of the S7-1200 station (the first slot to the left of the CPU).
3. Open the CM 1242-5 properties and assign the same PROFIBUS node address that the master has assigned to it. A mismatch will produce the bus-fault F-LED on the CM 1242-5 and "slave not found" / "station failure" diagnostics on the MVI56-PDPMV1. The node address is set in TIA Portal under CM 1242-5 > Properties > PROFIBUS address > Address, not on a physical DIP switch.
4. Configure the DP slave interface mode. The CM 1242-5 is always a DP-V0 slave; DPV1 services (acyclic read / write, alarm acknowledgement) are not available on this module. Do not enable DPV1 mode at the master for this slave.
5. Insert the I/O transfer areas. The CM 1242-5 supports up to 32 input bytes and 32 output bytes per direction in the typical configuration, but the slave may only see a subset depending on the master's slot/module configuration. The I/O areas are mapped to bit memory (M), process image inputs (I), process image outputs (Q), or data blocks (DB) in the S7-1200 CPU. Best practice is to map into a dedicated DB to avoid collisions with system flags and to ease diagnostic access from the user program.
6. Compile the S7-1200 project and download the hardware configuration to the CPU. The CM 1242-5 will not begin PROFIBUS exchanges until the master is also online and actively polling it; configuring and downloading the slave first is the correct order.

Step 3 - Match Data Areas: The Direction-Reversal Rule

The single most common configuration error on this integration is direction mismatch. PROFIBUS defines "input" and "output" from the master's perspective, and that perspective is the opposite of what an S7-1200 programmer writing transfer areas might assume:

• Master OUT = data the master writes to the slave = data the slave receives on its input area.
• Master IN = data the master reads from the slave = data the slave transmits from its output area.

Therefore, when the ProSoft master project declares an output module of, say, 8 words, the CM 1242-5 must declare a corresponding 8-word input transfer area in TIA Portal. Conversely, an 8-word input module in the ProSoft project is an 8-word output area at the CM 1242-5. The lengths must match line by line, but the direction reverses.

One engineering practice that prevents this confusion is to ask the Rockwell programmer for a screen capture of the ProSoft master project showing the slot table with I/O lengths. The slave configuration is then built in TIA Portal by mirroring that table with reversed direction. The ProSoft KB article 367 documents exactly this workflow for an S7-300 slave and the same workflow applies to the CM 1242-5.

Step 4 - Map the PROFIBUS I/O into Studio 5000 / Logix

The MVI56-PDPMV1 exchanges data with the ControlLogix processor over the backplane using an Add-On Instruction (AOI) provided by ProSoft. The PROFIBUS I/O slots configured in Step 1 are exposed to the Logix tag database as a block of INPUT and OUTPUT assembly instances.

1. Import the MVI56-PDPMV1 EDS into RSLinx (this is the only place the EDS is consumed - it has nothing to do with the S7-1200 side). The EDS is in the ProSoft downloads package for the MVI56-PDPMV1 and is registered with the RSLinx EDS Hardware Installation Tool.
2. Add the MVI56-PDPMV1 to the ControlLogix I/O tree under the local backplane. Right-click the 1756 backplane, select New Module, and choose the MVI56-PDPMV1. The Studio 5000 module selector uses the EDS catalog registered in step 1.
3. Select the connection size. The MVI56-PDPMV1 offers several connection sizes (commonly 248-byte input / 248-byte output, and smaller options). Choose a size that is at least as large as the total PROFIBUS I/O configured in Step 1; if the Logix connection is too small, the input assembly in Logix will read all zeros while the PROFIBUS side reports data exchange, which is a common first-time symptom.
4. Use the ProSoft AOI to copy the backplane input data into Logix tags the user program can read, and copy the Logix output tags into the backplane output image. The PROFIBUS master then ships the OUT data to the CM 1242-5 on the next cyclic exchange. The AOI is provided in the ProSoft downloads and is added to the project once via Import Add-On Instruction.
5. Add any required ladder logic to handle the data (scaling, handshaking, status word decoding, diagnostic interpretation). A typical pattern is to have a status word in the input image from the MVI56-PDPMV1 that the AOI maintains (heartbeat, PROFIBUS master state, slave state per node), and to use a control word in the output image for commands (clear diagnostics, reset counter, request slave ID).

Studio 5000 reports the connection to the MVI56-PDPMV1 as healthy when the backplane exchange is established. The PROFIBUS side becomes healthy only when the MVI56-PDPMV1 has the CM 1242-5 in its cyclic poll table and the slave is responding on the wire. The two are independent and must be verified separately.

Sample AOI wiring (representative)

The ProSoft AOI exposes a block of tags such as MVI56.InputData[N] and MVI56.OutputData[N]. The PROFIBUS input image (data read from the CM 1242-5 by the master) lands in MVI56.InputData; the output image (data to be written to the CM 1242-5 by the master) is read by the AOI from MVI56.OutputData. The AOI also maintains a status block with a heartbeat counter and a per-slave state array. Always refer to the AOI revision shipped with the firmware version of the MVI56-PDPMV1 you are using for the exact tag names.

Step 5 - Commissioning and Verification

1. Power up in the order: ControlLogix chassis, S7-1200, then any other PROFIBUS devices. Powering from one end of the segment helps the bus reach a stable state before termination settling is complete. Allow at least 5 seconds after the last device powers up before expecting data exchange.
2. Confirm the CM 1242-5 has the segment termination OFF (it is a drop, not a segment end), and that the two physical segment ends have termination ON. On standard 6ES7 972-0BA12-0XA0 PROFIBUS connectors, the termination switch is on the connector body.
3. On the CM 1242-5, observe the LED pattern. A solid RUN with no BF (bus fault) and a periodic flash on the DP communication LED indicates the slave is in data exchange. The exact LED labelling on the CM 1242-5 is on the front decal: ON (power), RUN, BF, MAINT.
4. On the MVI56-PDPMV1, open ProSoft Studio and view the PROFIBUS diagnostics. Each configured slave appears with its node address, current state (not connected / data exchange / diagnostic), and any slave diagnostics received via DPV1.
5. In Studio 5000, monitor the input assembly tags from the MVI56-PDPMV1. The data should be changing in step with the S7-1200 user program. Force a known value at the S7-1200 end and confirm it appears in Logix; force a known value at the Logix end and confirm it appears in the S7-1200 input area.
6. Capture the PROFIBUS diagnostics buffer in ProSoft Studio and confirm zero station-diagnostic frames, zero configuration-frame retries, and zero watchdog timeouts over a 10-minute soak.
7. Cycle power on the S7-1200 and confirm the MVI56-PDPMV1 logs a brief station-failure event followed by automatic re-entry into data exchange. This validates the auto-reconnect behaviour of the master.

LED and Diagnostic Interpretation

Troubleshooting Matrix

Baud Rate and Cable Length Reference

The baud rate must be the lowest common denominator of every device on the segment. A 12 Mbps master with a 1.5 Mbps slave will not communicate; PROFIBUS runs at one baud per segment. When mixing CM 1242-5 (which supports 9.6 kbps to 12 Mbps) with other slaves of different vintages, verify the slowest device first and lock the segment baud at that rate.

Node Address and Reserved Range

PROFIBUS reserves node addresses 0, 126, and 127 for special use. Address 0 is the default for a station that has not been configured; address 126 is the "no station" placeholder used by some configuration tools; address 127 is the broadcast address used by the master to reach all slaves simultaneously. The CM 1242-5 and the MVI56-PDPMV1 should both be configured with addresses in the 1 to 125 range, with each address unique on the segment. A duplicate address will cause both stations to fall into bus fault and the master will log configuration errors for both.

Common Engineering Pitfalls

• Importing the EDS into TIA Portal. The EDS is for EtherNet/IP. TIA Portal consumes the CM 1242-5 as a Siemens-native device from its hardware catalog; the GSD is only relevant on the ProSoft side.
• Forgetting to reverse the data direction. New integrators frequently configure the CM 1242-5 to send the data the master is supposed to send, and vice versa, producing configuration errors as soon as the master attempts to put the slave in data exchange.
• Mismatched node address. The CM 1242-5 is configured for its node address in TIA Portal (software), not on a physical DIP switch, so a download of a different TIA Portal project can change it without the field engineer noticing. Always re-verify the node address after a CPU project download.
• Exceeding 244 bytes cyclic per slave. The DP-V0 standard limits cyclic user data to 244 bytes IN and 244 bytes OUT per slave. Trying to configure larger areas will be rejected by the master or truncated by the slave's GSD.
• Bus terminator powered by slave that has lost CPU connection. Active terminators that source their power from the segment can mask termination; use passive terminating resistors on the end devices only.
• Mismatch between ProSoft I/O total and Logix connection size. If the Logix connection size is smaller than the total PROFIBUS I/O the MVI56-PDPMV1 is configured for, the input assembly in Logix reads zeros while the MVI56-PDPMV1 reports a healthy PROFIBUS exchange. Increase the Logix connection size in the module properties.
• Byte order. Logix INT and S7-1200 WORD are both 16 bits but the byte order inside the buffer may differ. Always verify with a known pattern (for example 0x1234) before assuming the data is correct.
• Watchdog timing. The S7-1200 user program must complete its scan within the PROFIBUS watchdog window or the slave will time out and the master will log a station failure. Increase the watchdog in the master project to 1-2 seconds if the S7-1200 scan time is variable.

Field-Proven Commissioning Sequence

1. Build the master project in ProSoft Studio with the CM 1242-5 GSD imported and a known I/O length (start with 4 words each direction as a smoke test).
2. Build the CM 1242-5 configuration in TIA Portal with mirrored lengths and reversed direction. Map the I/O into a dedicated DB (for example DB100 for inputs from master, DB101 for outputs to master) so the watch table is clean.
3. Bring up the segment with only the MVI56-PDPMV1 and the CM 1242-5, terminated at both ends. Add other slaves only after the master-slave pair is exchanging data.
4. Verify data in both directions with a simple echo test: Logix writes a counter to MVI56.OutputData[0], the S7-1200 reads it from DB100.DBW0, increments it, writes the result to DB101.DBW0, and Logix reads the result from MVI56.InputData[0]. Confirm the value increments at the expected rate.
5. Add the remaining segment slaves one at a time, re-verifying at each insertion that all slaves remain in data exchange and no new diagnostic frames appear in the ProSoft Studio buffer.
6. Capture and archive the ProSoft Studio diagnostics buffer, the TIA Portal online diagnostics for the CM 1242-5, and a Studio 5000 screenshot of the MVI56-PDPMV1 module properties for the as-built record.

Diagnostic Frame Format Reference

The CM 1242-5 emits PROFIBUS DP-V0 extended diagnostic frames when the S7-1200 user program writes to the diagnostic buffer. The format is byte 0 = status (0x00 = no fault, 0x01 = station not ready, 0x02 = station ready but fault in module, 0x80 = slave not ready, master must wait), byte 1 = master address, bytes 2..N = vendor-specific data. ProSoft Studio decodes this buffer and shows it in the slave's diagnostic pane. The Siemens DP-V0 extended diagnostic codes are listed in the CM 1242-5 manual and the STEP 7 / TIA Portal online help under PROFIBUS diagnostics.

Migration Notes: S7-300 to S7-1200 with the Same Master

Many plants are migrating from S7-300 with a CP 342-5 / CP 343-5 to S7-1200 with the CM 1242-5. The MVI56-PDPMV1 side does not change: the GSD for the CM 1242-5 is imported into the same ProSoft Studio project slot where the CP 342-5 GSD was. The node address, I/O lengths, and baud rate can be re-used verbatim. The TIA Portal side is built as a new station; the old STEP 7 V5.x project does not migrate automatically. Engineers should budget a day of bench testing for the S7-1200 replacement, plus a half day for on-site swap and verification, plus a half day for the as-built documentation refresh.

FAQ