System Overview
The SIMATIC TDC (Technology and Drive Controller) is a Siemens multiprocessor automation platform originally designed for high-speed drive, closed-loop, and technology applications in steel, paper, and printing machinery. The rack accepts a CPU551 processor module as the central application controller and slots CP5xxx communication modules next to it for PROFIBUS, Ethernet, and serial links. CP50M1 is the PROFIBUS-DP master module of the TDC family: it provides a class 1 DP-V0 master interface that can be used to attach Siemens and third-party DP slaves such as the legacy SIMATIC S5-class ET 200U distributed I/O station.
The source-described configuration stacks the following elements together:
- CPU551 — central TDC processor that runs the CFC/SFC chart for the application.
- CP50M1 — PROFIBUS-DP master in a free TDC slot, providing the link to the lower-level DP subnet.
- ET 200U with IM 318 (6ES5 318-8MB12) — DP slave interface for the S5-class I/O cluster.
- IM 316 (6ES5 316-8MA11) — passive interface that extends the S5 backplane bus into a sub-rack.
- 6ES5 470-8MA12 — 8-channel 12-bit analog output module.
- 6ES5 421-8MA12 — 32-channel digital input module.
The engineering question is whether this combination is supported, what the protocol on the IM 318 should be, and how the IM 316 (which is not a DP node) has to be handled in the TDC configuration. The remainder of the document is a field reference for that exact configuration.
Component Identification and Catalog Numbers
| Module | MLFB | Function | Slot / Location |
|---|---|---|---|
| CPU551 | 6DD1 600-0BB1 (range) | TDC processor, 64-bit RISC, 256 MB SDRAM | TDC rack, central slot |
| CP50M1 | 6DD1 660-0BA1 | PROFIBUS-DP master (DP-V0, 12 Mbit/s max) | TDC rack, communication slot |
| IM 318-8 | 6ES5 318-8MB12 | DP slave interface for ET 200U | ET 200U rack, leftmost module |
| IM 316 | 6ES5 316-8MA11 | Centralized I/O bus extension (S5 sub-rack link) | ET 200U expansion sub-rack, slot 0 |
| AO 8x12 bit | 6ES5 470-8MA12 | Analog output | S5-135U/155U compatible slot |
| DI 32 | 6ES5 421-8MA12 | Digital input | S5-135U/155U compatible slot |
The 6ES5 318-8MB12 (suffix -8 = PROFIBUS-DP, -MB = standard product version) is the PROFIBUS-DP variant of the IM 318 family. The earlier -8MA11 suffix does not support DP. The CP50M1 is the standard DP master for TDC, distinguishable from the CP50M0 by its DP-V1 capability. If the TDC has a firmware variant that ships with a CP51M1 (PROFINET) only, the CP50M1 must be ordered separately and licensed on the rack.
Compatibility Assessment
The combination is supported with the following points verified against Siemens documentation:
- Master side (CP50M1) — the CP50M1 acts as a class 1 PROFIBUS-DP master on the TDC backplane. It accepts any DP-V0 slave that exposes a type-3 or type-4 GSD. The ET 200U with IM 318-8MB12 conforms.
- Slave side (IM 318-8MB12) — the Siemens support entry 217419 confirms that the IM 318-8MB12 (and its -8MB13 successor) supports either the DP-SIEMENS protocol or the DP standard (EN 50170) protocol. The choice is set by the rotary switch on the module or by the configuration tool that downloads the parameter set to the slave.
- I/O modules — the 6ES5 470-8MA12 and 6ES5 421-8MA12 are S5-135U/155U I/O modules and are accepted in the ET 200U rack as long as the IM 318 firmware version (V3.0 or later for the -8MB12 variant) recognizes them. Confirm the IM 318 firmware using the S5 PG and the "Module Information" readout, or via the CP50M1 diagnostic read during a live bus scan.
- IM 316 role — the 6ES5 316-8MA11 is not a DP node. It is a passive bus extender that forwards the S5 backplane signals (SA-/SB-bus) to a sub-rack. It must be slotted in the same logical rack as the IM 318 and does not appear in the PROFIBUS configuration as a separate node.
DP-SIEMENS vs DP Standard Protocol
The IM 318-8MB12 supports two protocol families. The choice affects how the I/O is mapped into the TDC process image and which GSD file is loaded into the engineering tool.
| Property | DP-SIEMENS | DP Standard (EN 50170) |
|---|---|---|
| GSD identifier | SIEM8041.GSD (typical for -8MB12) | SIEM8042.GSD or any DP-V0 standard GSD |
| Module mapping | Slot-based, fixed-length I/O per slot | Slot-based, flexible module lists |
| Diagnostic model | Siemens-extended diagnostics (DPV0 ext.) | Standard EN 50170 diagnostics |
| Interoperability | Siemens master preferred (CP50M1 ideal) | Any DP-V0 master accepted |
| Recommended use | Native S5 environment with Siemens tooling | Mixed-vendor environment |
When CP50M1 is the master, either protocol works. The factory default of the IM 318-8MB12 is DP-SIEMENS. To switch, use the S5/DCOM configuration tool and set the rotary switch on the IM 318 to position 0 for standard DP, position 1 for DP-SIEMENS, then re-parameterize the slave with a CP50M1 download. The change is volatile unless stored to the IM 318 flash via the "Save Parameters" function of the S5 tool.
DP Cycle Time Calculation
For sizing the bus, use the following approximations. With the IM 318-8MB12 publishing the 6ES5 421-8MA12 (4 bytes DI) and the 6ES5 470-8MA12 (16 bytes AO), the cyclic I/O payload is 20 bytes per station. At 1.5 Mbit/s:
- Bit time:
T_bit = 1 / 1.5e6 = 666.7 ns - Byte time (11-bit UART):
T_byte = 11 * 666.7 = 7.33 us - DP frame overhead (SD, DA, SA, FC, DU, FCS, ED): ~ 11 bytes header + 3 bytes trailer = 14 bytes
- Total frame size:
14 + 20 = 34 bytes - Frame transfer time:
34 * 7.33 us = ~ 250 us - Plus token rotation, slave processing (~ 1 ms typical for IM 318-8MB12), and acknowledge gap: typical cycle 1-2 ms at 1.5 Mbit/s
At 12 Mbit/s the same frame drops to ~ 31 us, but the cable length limit drops from 200 m to 100 m, and the S5-135U/155U I/O modules with longer debounce filters may not deliver improvements at the application layer. For most TDC + ET 200U retrofits, 1.5 Mbit/s is the safe default.
Hardware Configuration Procedure
Follow this sequence in the TDC engineering tool (D7-SYS, formerly CFC-SFC):
- Slot the hardware. Insert the CPU551 in the TDC processor slot. Insert the CP50M1 in a free communications slot. Verify the backplane connector seating and the supply voltage (TDC requires 24 V at the rack; CP50M1 draws ~ 1.5 A typical).
- Configure the rack. Open the rack view in D7-SYS. Assign the CPU551 its rack address (default 0). Assign the CP50M1 a unique address within the rack (any unused slot 1..56). The slot is a logical address used by the CPU551 to talk to the CP50M1 across the TDC backplane.
- Insert the GSD. Copy the appropriate GSD for the IM 318-8MB12 (DP-SIEMENS: SIEM8041.GSD; DP standard: SIEM8042.GSD) into the GSD directory of D7-SYS. The file comes from the Siemens Industry Online Support portal under the ET 200U product tree.
- Configure the DP subnet. In the CP50M1 properties, declare a new PROFIBUS subnet. Set the transmission rate to 1.5 Mbit/s (the IM 318-8MB12 supports up to 12 Mbit/s; 1.5 Mbit/s is the safe default for cable lengths above 200 m and for the S5-135U I/O mix).
- Insert the IM 318 slave. Add a DP-V0 slave, paste from catalog, set its PROFIBUS address to a unique value (avoid 0..2; pick e.g. 6). The slave will offer slot 1 = the I/O modules declared.
- Insert the I/O modules. In slot 1 of the IM 318, add the 6ES5 421-8MA12 (32 DI, 4 bytes input). In slot 2 add the 6ES5 470-8MA12 (8 AO, 16 bytes output). The order in the slot list determines the byte offset in the TDC process image.
-
Map the I/O into the CFC. In the CFC chart, allocate the input bytes 0..3 to a process tag block (e.g., CH_AI/CH_DI) and the output bytes 0..15 to the AO block. The CP50M1 publishes the cyclic I/O as global process variables with names like
CP50M1.IN[0..3]andCP50M1.OUT[0..15]. - Compile and download. Compile the rack configuration. Download the configuration to the TDC rack. Power-cycle the ET 200U only if the IM 318 reports parameter errors (the BUSF LED toggles at 0.5 Hz).
IM 316 Role and Wiring
The IM 316-8MA11 bridges the S5 backplane bus of the ET 200U sub-rack. It is wired with the standard S5 sub-rack bus cable (6ES5 706-0AAxx, length variants 0.5 m, 1.0 m, 1.6 m, 2.5 m). Pin-out follows the S5-135U convention:
- SA bus: rows 1-32 of the S5 connector (front-plane I/O addressing)
- SB bus: address lines for I/O slot identification
- PG-/OP-/SYN-/ARB- lines: arbitration across the rack chain
Place the IM 316 in slot 0 of the sub-rack (the standard "interface" position). The IM 318 must be in slot 0 of the master rack. The two sub-racks are then chained with a 6ES5 706 bus cable. Do not attempt to address the IM 316 as a separate DP node — it has no PROFIBUS interface.
I/O Module Range Configuration
The two I/O modules are fixed-range, not configurable over PROFIBUS:
| Module | Channels | Resolution | Range setting | Notes |
|---|---|---|---|---|
| 6ES5 470-8MA12 | 8 AO | 12 bit | Solder bridges on side panel (0-10 V, +/-10 V, 0-20 mA, 4-20 mA, +/-20 mA) | All 8 channels share the same range; mixed ranges require two physical modules. |
| 6ES5 421-8MA12 | 32 DI | n/a | Solder bridge for P-reading (factory default) or N-reading | Organized as 4 groups of 8; 24 V sensor supply must be applied to the L+ terminal of each group. |
Because the ranges are hardware-selected, the PROFIBUS configuration only declares the number of bytes (4 DI bytes, 16 AO bytes) and the slot order. No parameter record is sent to the modules themselves; the IM 318 does not act on any module-level parameterization for these two MLFBs.
Verification
After download, perform these checks in sequence:
- On the CP50M1, the PROFIBUS status LED must be solid green (RUN). If flashing at 2 Hz, the bus is starting; if dark, the master is not active.
- On the IM 318, the BUSF LED must be dark and the RUN LED solid green. A flashing BUSF (2 Hz) means the slave is offline; a steady BUSF means parameter assignment error.
- In D7-SYS, open the online view of the CP50M1 and read the cyclic I/O image. Forcing a known state on the 6ES5 421-8MA12 input must reflect in the CFC chart within one DP cycle (typically 1-5 ms at 1.5 Mbit/s).
- Force a 0 V output on the 6ES5 470-8MA12 with a 4-20 mA load. The measured current must track the forced value within +/- 0.5% of full scale (12-bit DAC, LSB = full scale / 4096).
- Check the diagnostic buffer of the IM 318. Any entry "Identifier byte error" or "Configuration error" points to a slot mismatch between the GSD declaration and the physical module.
- Verify the IM 316 is recognized by the IM 318 by reading the IM 318 diagnostic frame. A healthy IM 316 chain reports "extension OK" in slot 0 of the sub-rack; a missing IM 316 reports "extension fault" in the same slot.
Troubleshooting Matrix
| Symptom | Probable Cause | Action |
|---|---|---|
| IM 318 BUSF LED flashing 2 Hz | PROFIBUS cable break, missing termination, or address conflict | Check PROFIBUS connector seating. Verify the slave address in D7-SYS matches the rotary setting on the IM 318. Confirm termination resistor is ON at both physical ends of the segment, OFF in the middle. |
| IM 318 BUSF LED steady | Parameter or configuration mismatch | Compare slot list in D7-SYS with the modules physically inserted. Re-download configuration. Verify the protocol switch (DP-SIEMENS vs DP standard) matches the GSD you loaded. |
| IM 316 not recognized in S5 tool | Wrong slot or missing bus terminator | Verify IM 316 in slot 0 of sub-rack. Set terminator ON only on the last rack. Inspect the 6ES5 706 bus cable for bent pins. |
| IM 318 not in hardware catalog | GSD file not installed or wrong directory | Copy the IM 318-8MB12 GSD into the D7-SYS GSD directory. Restart the engineering tool. Verify file permissions allow the tool to read the GSD. |
| CFC chart sees no I/O update | Slot mapping offset error or CP50M1 not licensed | Verify byte offset in the CP50M1 process image. Cross-check the input address in the CFC tag declaration. Verify the PROFIBUS-DP master license bit is set on the TDC rack. |
| AO 6ES5 470-8MA12 outputs frozen at 0 V | Wrong output group enabled, or load wire break | Check the "enable" bit for the relevant channel group. Verify load wiring (floating load required for voltage output; current output requires a passive load to GND). |
| DI 6ES5 421-8MA12 reads stuck at 0 | Sensor power not supplied, or wrong P-reading (NPN/PNP) | Apply 24 V to the sensor supply terminals. Verify input group is configured for P-reading if sourcing sensors are used. For sinking sensors, change the solder bridge to N-reading. |
| CP50M1 RUN LED dark | CP50M1 not licensed or not configured | Verify the CP50M1 is in the rack configuration. Verify the TDC license includes PROFIBUS-DP master option. Check the TDC firmware version supports the CP50M1 variant ordered. |
| IM 318 reports "station failure" during runtime | EMI on the PROFIBUS cable or sub-D connector loose | Tighten the sub-D connector screws. Check shield bonding at both ends of the PROFIBUS cable. Verify the cable is not run parallel to VFD power cables for more than 1 m. |
| CFC I/O values are correct but oscillate between two states | DP cycle jitter from high bus load | Reduce PROFIBUS bus load. If more than 16 slaves are on the segment, split the network. Set the CP50M1 watchdog to a value 3x the measured cycle time. |
Firmware and Documentation References
- IM 318-8MB12 firmware is typically V3.x for the 8MB12 and 8MB13 variants. Earlier firmware (V2.x) does not support all S5-135U/155U I/O modules. The firmware version is printed on the module side label as "FW: V3.x.x".
- CP50M1 firmware is part of the TDC base load. Update through the TDC firmware update tool (D7-SYS Online → Firmware Update). The CP50M1 firmware version is shown in the module information dialog and is also reported in the rack diagnostic.
- For VMware vSphere compatibility of TDC engineering stations, consult the Broadcom Compatibility Guide entry for Siemens AG. Not all TDC runtime versions are supported under ESXi 7.0 U3; verify before deploying a virtual engineering host to avoid rack-communication issues during commissioning.
- The Siemens support entry 217419 documents the DP-SIEMENS / DP standard selection on the IM 318-8MB12 and -8MB13. It is the authoritative reference for the protocol choice.
Notes and Caveats
- The IM 316-8MA11 will not appear in the PROFIBUS hardware catalog. It is configured only in the S5-135U/155U sub-rack context, and is invisible to the DP master.
- If the application requires DP-V1 (acyclic record access, e.g., for parameterizing the AO module), confirm that the IM 318-8MB12 firmware supports DP-V1. The -8MB12 is generally DP-V0 only; the -8MB13 added DP-V1 extensions for diagnostic and parameter data.
- Maximum cable length for PROFIBUS at 1.5 Mbit/s is 200 m with standard cable (Siemens 6XV1 830-0AH10 or equivalent). For 12 Mbit/s, the limit drops to 100 m. Repeaters can extend the bus but increase token rotation time.
- The 6ES5 470-8MA12 is an 8-channel 12-bit analog output. Output ranges (0-10 V, +/-10 V, 0-20 mA, 4-20 mA, etc.) are selected via solder bridges on the module side panel. Range configuration is not done via PROFIBUS. Mixed ranges on the same module are not supported.
- The 6ES5 421-8MA12 is a 32-channel digital input, organized in 4 groups of 8. P-reading (sourcing) is factory default; N-reading requires a solder bridge change on the module.
- Power supply for the ET 200U rack: 24 V at 5 A minimum, with sufficient headroom for the AO 6ES5 470-8MA12 when driving 4-20 mA loops into short-circuit-protected loads.
- When replacing the IM 318-8MB12 with a -8MB13 spare, the GSD file is compatible but a re-download of the slave parameters is required.
FAQ
Does the IM 316-8MA11 appear in the PROFIBUS hardware catalog of the TDC CP50M1?
No. The IM 316-8MA11 is a passive S5 sub-rack extender with no PROFIBUS interface. It is invisible to the DP master. The CP50M1 sees only the IM 318-8MB12 and the I/O modules that the IM 318 publishes on DP.
Which protocol should I select on the IM 318-8MB12 — DP-SIEMENS or DP standard?
For a CP50M1 master with no mixed-vendor requirement, use DP-SIEMENS (factory default). Use the matching GSD: SIEM8041.GSD for DP-SIEMENS, or SIEM8042.GSD for DP standard. The choice is set by the IM 318 rotary switch and a configuration download from the master, and is documented in Siemens Support entry 217419.
What is the maximum PROFIBUS transmission rate with the IM 318-8MB12?
The IM 318-8MB12 supports up to 12 Mbit/s. For mixed S5-135U/155U I/O and cable runs above 200 m, use 1.5 Mbit/s as a safe default. For shorter, controlled installations with quality PROFIBUS cable, 12 Mbit/s is permissible and drops the cyclic I/O update to ~ 100 us per station.
Can I configure the I/O modules (6ES5 470-8MA12, 6ES5 421-8MA12) via PROFIBUS?
No. Both modules are fixed-range analog/digital I/O. Output range (for 470) and input direction (for 421) are set by hardware solder bridges on the module itself, not by PROFIBUS parameters. Use the GSD slot declaration only for I/O length, not for range configuration.
Where can I obtain the official IM 318-8MB12 GSD file?
The GSD files for the IM 318-8MB12 (SIEM8041.GSD, SIEM8042.GSD) are available from the Siemens Industry Online Support portal under the ET 200U product tree. The compatibility entry for the DP interface is documented in Siemens Support entry 217419, which is the authoritative reference for this module family.