Configuring MasterDrive MC Virtual Master Position over Profibus

Problem Definition: Cross-Vendor Master Position Distribution

The engineering challenge is to forward a single Siemens SIMOVERT MASTERDRIVES MC virtual master position to a non-Siemens motion drive (for example, a Bosch Rexroth IndraDrive controlled by an ABB AC500 PLC) while keeping the existing 38-axis Simolink ring and S7-319 Profibus cluster intact. The non-Siemens side does not run Simolink fiber, does not run DriveMonitor, and cannot import a Siemens-specific GSD for a class 1 master role from the same vendor ecosystem. Three practical export paths exist: a second CBP2 channel on the originating MasterDrive MC, an SLE Simolink encoder module that produces a hardware incremental RS422 stream, or a Profibus / Profinet / real-time Ethernet gateway. Each path has distinct latency, resolution, and isochronous limitations, which the following sections quantify.

Reference System Architecture

The reference installation consists of:

• 38 × SIMOVERT MASTERDRIVES MC (6SE70 series) with vector control firmware for rotary axis applications.
• One SLB (Simolink Board) per drive, forming a closed fiber-optic ring (plastic or HCS, 850 nm). The Simolink cycle time is configured between 0.4 ms and 6.4 ms in the master drive, with 1.0 ms being the field-default for rotary axis synchronization.
• 38 × CBP2 (Communication Board Profibus 2) on an S7-319 (6ES7318-3EL01-0AB0 or compatible) Profibus DP segment running at 1.5 Mbit/s or 12 Mbit/s.
• One MasterDrive MC is configured as the Simolink master and the source of the virtual master position. The virtual master position is computed inside that drive from P481 (master enable), P482 (position source), and P483/P484 (gear scaling) and is broadcast to the ring.
• The Bosch Rexroth motion drive is commanded by an ABB AC500 PLC. The drive supports Profibus DP slave, Profinet IO, and SERCOS III. The drive can also act as a DP class 1 master for downstream devices.

All 38 drives, the originating CBP2, the S7-319, and the Simolink topology are documented in the SIMOVERT MASTERDRIVES compendium and the option board operating instructions available on the Siemens Industry Online Support portal (see SIMOVERT MASTERDRIVES Compendium and SIMOVERT MASTERDRIVES Option Boards Operating Instructions (AC, 05.2006)).

Integration Paths: Three Engineering Options

Option A — Add a Second CBP2 and Make the Non-Siemens Drive the DP Class 1 Master

The originating MasterDrive MC can host two CBP2 boards. Slot 1 (left) and Slot 2 (right) are accessed through parameters r826.0 and r826.1 respectively, as documented in the application note Connecting SIMOVERT MASTERDRIVES MC to the Technology-CPU. With a single CBP2 the bus identification is r826.0; with a second CBP2 inserted the monitoring tree extends to r826.1 and the second board appears in DriveMonitor under Communication / CBP2 / Slot 2. The bus address is set on the CBP2 DIP switches (1 – 125) and the bus parameters are then controlled by the class 1 master through the standard DP-V1 acyclic services on the second slot.

DP-V1 vs DP-V2: Why Isochronous Mode Is Not Available

The CBP2 firmware supports Profibus DP-V0 and DP-V1 only. DP-V2 introduces the isochronous mode (clock-driven, jitter < 1 µs) and slave-to-slave broadcast. The CBP2 hardware can technically process DP-V2 isochronous frames, but the field-proven limitations are:

1. Siemens does not publish a DP-V2 GSD for the CBP2. The latest GSD shipped in the DriveMonitor / SIMOVERT MASTERDRIVES option board package is SIEM8115.GSD, which is DP-V1 only.
2. The isochronous configuration in the master PLC is supplied by SIMATIC STEP 7 with the Siemens-specific GSD revision. A non-Siemens class 1 master (Rexroth / ABB) cannot import the Siemens isochronous slot definition, so it cannot clock the CBP2 in DP-V2 isochronous mode.
3. Consequence: when a non-Siemens master polls the second CBP2, the bus runs in DP-V1 — free-running, no clock, no isochronous guarantee.

GSD File Selection and Class 1 Master Constraints

For the second CBP2 acting as a DP-V1 slave to the non-Siemens master, install SIEM8115.GSD on the Rexroth / ABB engineering station. The GSD identifies the slave as a SIMOVERT MASTERDRIVES CBP2 and exposes the standard PPO types 1, 2, 5 (4 bytes PKW + 4/8 bytes PZD) and the modular slot 0/1/2 structure. Process data are PZD1 / PZD2 in slot 1 (setpoint / actual value) and PKW for parameter access. PZD wiring inside DriveMonitor:

The 4-byte position transfer uses two consecutive PZD words; configure slot 1 as 2 words in, 2 words out in the GSD module list. The class 1 master on the non-Siemens side must support a "modular station" with the number of PZDs selected from the GSD. Both IndraWorks (Rexroth) and ABB Automation Builder support this for any compliant DP-V1 slave.

Throughput Estimate on a 12 Mbit/s DP Segment

For a 1-master / 1-slave segment at 12 Mbit/s, the DP bus cycle is bounded by T_bit = 0.0833 µs and the protocol overhead of approximately 220 bits per token + telegram. The 8-byte I/O payload (2 words in + 2 words out) is ~96 bits payload per cycle. Field-measured bus cycle for this configuration is ≈ 0.5 – 1.0 ms. Position update latency = 1.0 – 2.0 ms plus the master-drive scan time of 1 ms. Total: 2 – 3 ms end-to-end. This is acceptable for a position read-back and for a slow electronic cam; it is not acceptable for an electronic gear that must phase-match a 1 ms Simolink cycle.

Option B — SLE Simolink Encoder Module (Incremental RS422 Output)

The SLE is a Simolink-resident encoder emulator. It taps the Simolink ring and outputs a hardware incremental A/B/N signal in RS422 (differential, 5 V line) at a fixed pulse count of 8192 increments per Simolink revolution. The module is wired in place of an external encoder: the receiving Rexroth drive (or any third-party controller) reads the A/B pulses exactly as it would read an Indradyn or Heidenhain encoder. The SLE is part of the option board family listed in the SIMOVERT MASTERDRIVES Option Boards Operating Instructions (AC, 05.2006) (CBP/CBP2 – CBC – SLB – EB1 – EB2 – SBP – SBR1/2 – SBM family, with SLE as the encoder variant of the Simolink board).

Position Resolution and Gear Matching

8192 pulses per revolution is 13 bits of resolution per hardware turn. With 4-quadrant decoding (X4) the effective count is 32 768 increments per mechanical turn. The Bosch Rexroth IndraDrive encoder input is typically configured to 8192 or 16384 lines/rev in IndraWorks; the SLE is set (by Simolink configuration) to 8192 ppr. The receiving drive treats the SLE pulses as a master reference and computes the position by counting edges:

θ_rex [increments] = SLE_pulses × GearRatio × LoadGear

GearRatio is the electronic gear factor set in the Rexroth drive (S-0-0032 / S-0-0033 / S-0-0034 in SERCOS terminology, or P-0-0072 / P-0-0073 in Profibus parameter form).

Wiring and Signal Levels

Use a shielded twisted pair (e.g., Belden 9841 or 8102) with characteristic impedance 120 Ω, terminated with 120 Ω at the receiving end only (the SLE provides internal termination). Maximum cable length for RS422 at 1 MHz edge rate is approximately 50 m; field practice is to keep this under 25 m for noise margin.

Option C — Profibus / Real-Time Ethernet Gateway

If the receiving side runs Profinet, EtherCAT, or SERCOS III instead of Profibus, deploy a gateway such as a Helmholz DP/PN coupler (700-158-3AA02) or a Siemens DP/PN IO gateway (e.g., 6ES7158-3AD10-0XA0). The gateway appears as a DP-V1 slave on the MasterDrive side (using the same SIEM8115.GSD) and as a Profinet / EtherCAT slave on the ABB side. Throughput is 4-byte process data, latency 2 – 4 ms, no isochronous mode. This is the right answer when the receiving drive does not have a Profibus option and a free RS422 encoder input is not available.

MasterDrive MC Parameter Set for Virtual Master Export

The virtual master is configured inside the Simolink master drive. The minimum parameter set for the export channel is:

For Option B (SLE) the parameters P601 – P605 are not used; the Simolink configuration is unchanged and the SLE module is configured via its own rotary switches for node address and base pulse count.

Commissioning Procedure — CBP2 Path

1. Power down the master drive. Insert the second CBP2 into the right slot. Verify the board is recognized: r826.1 must display "CBP2 Vx.xx". CBP2 firmware ≥ V2.20 is recommended for stable operation with non-Siemens masters; older V1.xx firmware has known issues with acyclic DP-V1 services on slot 2.
2. Set the bus address DIP switch to 3 (or any unused address on the segment).
3. Connect a shielded Profibus cable from the CBP2 X4 (9-pin DSUB) to the non-Siemens master's Profibus X4. Apply 120 Ω termination at both physical ends only.
4. Import SIEM8115.GSD into the non-Siemens engineering tool. Add a DP-V1 slave at address 3 with PPO type 2 (or modular with 2 PZD in / 2 PZD out).
5. Configure the receiving drive to read the 4-byte cyclic output from PZD1 / PZD2. Map the value to a position variable in the ABB PLC.
6. Start the Simolink ring. Check r826.1 in DriveMonitor — state must be "Data Exchange".
7. Toggle the virtual master on the source drive and verify the position value in the ABB PLC increments at the configured ramp.
8. For diagnostic tracing, read r551 (process data word) on the MasterDrive and the corresponding cyclic input on the non-Siemens master.

Commissioning Procedure — SLE Path

1. Insert the SLE into the Simolink ring (fiber loop in / out). Verify the SLE is recognized as a Simolink node and that the address set on its rotary switch (for example, node 60 — any unused address) is consistent with the Simolink master configuration.
2. Configure the SLE pulse count (8192 ppr) and the zero-pulse behavior (one N pulse per virtual master revolution) via the SLE service tool or via the parameter P-SLE-001 (vendor-specific).
3. Wire the SLE X4 (RS422 A/B/N) to the IndraDrive encoder input X4. Set the encoder type in IndraWorks to "incremental, 8192 lines, RS422".
4. Power the SLE from the 24 V supply on the encoder connector (pin 7/8) or from an external 5 V source if the Rexroth connector is wired for 5 V encoder supply only.
5. Run a homing routine on the Rexroth drive to the first N pulse after power-up. The drive will be referenced to the virtual master zero position.
6. Test with a slow Simolink ramp; verify that the Rexroth drive follows the position ramp in IndraWorks trace.
7. Set the electronic gear ratio in the Rexroth drive to match the desired mechanical ratio. The internal position is the SLE pulse count multiplied by the gear ratio.

Verification and Diagnostics

On the non-Siemens side, the IndraDrive parameter S-0-0144 (interface status) or P-0-0800 (comm status) reports "OK" once DP data exchange is established. If the state stays at "Wait for Param" or "C1 Master missing", the GSD is the wrong revision or the bus address conflicts with another node on the segment.

Common CBP2 Fault Codes

Simolink LED and Status Word

On the SLB (Simolink Board) the green "LINK" LED is on when the fiber ring is closed. The "DATA" LED flickers on every successful ring cycle. r822 reports the Simolink state (0 = RUN, 1 = SYNC lost, 2 = ring break). A cyclic read of r822 is the most reliable way to detect a broken fiber in real time.

Performance, Latency, and Field Caveats

Measured round-trip latency on a reference installation with one CBP2 + non-Siemens master at 12 Mbit/s:

• DP bus cycle: 0.5 – 1.0 ms
• MasterDrive MC scan time: 1.0 ms (cycle 2 of the drive)
• Non-Siemens controller scan time: 2.0 ms (IndraDrive control cycle)
• End-to-end position update: 3.0 – 4.0 ms

For Option B (SLE) the same end-to-end latency is dominated by the Simolink cycle (1 ms) plus the encoder latch in the Rexroth drive (typically 250 µs) plus the drive's own control cycle (1 ms): about 2.25 ms end-to-end. The advantage of Option B is that the latency is bounded by hardware clock edges, not by bus scheduling; the jitter is sub-microsecond, which is the requirement for electronic gearing.

All three configurations have been commissioned on real installations; in the rotary-axis application described here, the SLE path was selected because the Rexroth drive is required to run an electronic cam from the virtual master. The CBP2 path was kept as a backup diagnostic channel for slow position readback only.

Frequently Asked Questions