Troubleshooting IM308-B PROFIBUS Master EPROM Programming on S5

System Overview: IM308-B as PROFIBUS Master on SIMATIC S5

The Siemens IM308-B (order number 6ES5308-3UB11) is a PROFIBUS-DP master module for the SIMATIC S5-115U, S5-135U, and S5-155U PLC families. It occupies one slot in a standard S5 rack and is recognized by the AG (automation device) as an intelligent coprocessor. The master runs a DP-V0 class-1 service and exchanges process data with DP slaves over a shielded twisted-pair PROFIBUS cable, terminated with 9-pin D-sub connectors and bus terminators at both line ends.

The IM308-B has its own operating mode selector, a status LED block (RN / ST / IF / BA / SD / RD), and a memory-card slot on its front bezel. The slot accepts one EPROM or EEPROM submodule of the 6ES5375-1xxxx family, which holds the slave configuration database (the GSD-derived configuration image) plus the bus parameters. At PLC power-up the IM308-B copies the configuration from the memory card into its dual-port RAM, then starts the bus.

The configuration image is generated offline on a PG/PC using COM PROFIBUS (older name: COMET200) and is then written to the EPROM. Once programmed, the EPROM is inserted in the IM308-B and the master can be replaced or cold-started without losing its bus database — an essential feature for maintenance and field replacement.

Hardware Configuration Reference

The following parts list reflects a working reference configuration. All catalog numbers are Siemens MLFBs and can be cross-referenced against the current Siemens Industry Online Support portal.

COMET200 / COM PROFIBUS Configuration Procedure

Configuration is performed offline with COM PROFIBUS V5.1.2.2 (COMET200). Launch the tool, create a new project, and step through the following screens.

F1 — ET200 System Parameters

F2 — Slave Configuration

For the ET200U at station 3, configure the slot map exactly as the physical hardware installed. An incorrect slot map is the most common cause of a slave not coming online, even with a valid GSD file.

Station number : 3
Area          : P  (peripheral)
Station type  : ET200U
Station name  : et200u_station_3

Next available address  DI : 10   DQ : 11   AI : 0    AQ : 0

Configuration:
   Slot | Module | I address | Q address
   -----+--------+-----------+----------
    0   | 8 DQ   |   1.000   |    —
    1   | (empty)|    —      |    —
    2   | (empty)|    —      |    —
    …
    31  | (empty)|    —      |    —

Save the project as C:\TEST01\ET.200. The file extension .200 is the native COMET200 configuration file.

CPU User Program for Loopback Test

Before debugging PROFIBUS, program the CPU with a minimal loopback so the engineer can verify that I/Q addressing is correct. A one-line OB1 is sufficient:

// OB1 – Cycle
      L    IB    0           // Read inputs from digital input module 6ES5430
      T    QB   10           // Mirror onto digital output module at Q 10.0
      BE

When PROFIBUS is healthy, the digital-output LEDs on the ET200U should follow the digital-input LEDs on the S5-115U rack. If they do not, the failure is in the bus, not the application code.

EPROM 6ES5375-1LA21 Programming Methods

There are three documented paths for moving the COMET200 configuration into the 6ES5375-1LA21 EPROM. Each path uses a different tool chain and each has its own failure modes.

Method A — Direct programming from COMET200 menu F3 (in-system programmer)

1. Open the saved .200 project in COMET200.
2. From F3 — Transfer functions select Transfer partner: E(E)PROM / File.
3. From F1 — Programming of memory submodule enter programming number 412 for the 6ES5375-1LA21.
4. Insert the EPROM in the in-system programmer attached to the PG.
5. Click Start.

Failure mode: "Wrong submodule or no submodule plugged in" — see Troubleshooting section.

Method B — Convert project to binary file, then program with STEP 5 EPROM Programming tool

1. In COMET200 F3, choose F4 — Program file → Binary file and save as A:\TEST01\BN.200.
2. Transfer BN.200 to a PG with STEP 5 V7.23 and the USB-PROMMER 6ES7792-0AA00-0XA0 installed.
3. Start Start → Simatic → STEP 5 → S5 Eprom (application STEP5 EPROM Programming V1.0).
4. From the Module menu select Load from binary file, browse to A:\TEST01\BN.200, set Block A, programming number 412, mode BYTE.
5. Insert the 6ES5375-1LA21 into the USB-PROMMER socket and click Start.
6. Confirm the prompt Binary file transferred to module — write cycle takes 60 – 90 s for 256 KB.

Method C — Classic DOS programmer under STEP 5 project environment

For older PGs without USB:

1. Open the STEP 5 project containing the COMET200 export.
2. From STEP 5 → File → Project → Set → 6 EPROM configure the EPROM target (programming no. 412, type 6ES5375-1LA21).
3. From Management → EPROM Handling, select Write and follow the prompts.

Resolving "Wrong Submodule or No Submodule Plugged In"

This is the most common error encountered and has several independent root causes. Apply the remedies in the order listed.

IM308-B LED Diagnostics and Startup Behaviour

After the EPROM is verified, install it in the IM308-B with the PLC powered off, mode switch on the IM308-B in ST (Stop). Power on and wait for the CPU to complete its start-up. Then move the IM308-B switch to RN (Run). The expected LED pattern is:

The reported symptom — ST blinks, IF stays on, BA off, no data exchange — corresponds to initialisation failure or configuration mismatch. Treat it as a comparison between the EPROM image and the physical bus, not a hardware defect on the IM308-B.

DP Standard vs Siemens DP Protocol Selection

When the IM308-B is configured as a master, the bus profile must be selected as either DP – Standard (PROFIBUS-DP, IEC 61158/EN 50170) or Siemens DP (the older proprietary subset). For all third-party slaves and any slave whose GSD declares DP-V0 compliance, the profile must be DP – Standard.

For the older Siemens DP slaves such as the IM318-B, a profile mismatch is a frequent source of ST blinks + IF on:

• Set the DP / Standard DP selector on the IM318-B DIP switch block to match the value programmed into the IM308-B EPROM.
• Verify the setting visually with the IM318-B's own status LEDs; a flashing red SF LED indicates a profile conflict.

When the system contains a mix of ET200U and IM318-B slaves, the safest engineering choice is to set both switches to Standard DP and keep all configuration in the COMET200-native .200 database.

Verification Procedure

1. Power up the PLC, CPU reaches RUN, IM308-B in ST.
2. Move IM308-B switch to RN. Confirm LED pattern reaches BA on, SD/RD flicker within 20 s (matches the 20 s power-up delay).
3. Force a digital input at the S5 rack input module 6ES5430. The corresponding bit on the ET200U-side digital-output module 6ES5441 should toggle within one OB1 cycle (typically 20 – 100 ms).
4. Use COM PROFIBUS online Live List to confirm that station 3 (ET200U) is in data exchange and not in diagnostic state.
5. Remove and reinsert the EPROM, repeat steps 1 – 4. The configuration should be identical, demonstrating that the database is stored in the EPROM and not in volatile RAM.

Troubleshooting Matrix

Field-Proven Caveats

• EPROMS are one-time-programmable only with the USB-PROMMER's high-voltage programming algorithm. The device must have a quartz window (the "windowed" variant of 6ES5375-1LA21) to be UV-erasable. OTP variants are field-replaceable but not field-reusable.
• COMET200 versions are not interchangeable with all STEP 5 versions. The 6.x and 7.x STEP 5 baselines ship with an updated EPROM driver table. If the table does not list the 6ES5375-1LA21, the binary-export method (Method B) is the reliable workaround.
• PG720/PG740 with STEP 5 V2.3 is documented to produce the same "Wrong submodule" message. Upgrading to STEP 5 V6.5 or V7.23 with the S5Toolbox typically resolves it.
• Power-up delay in COMET200 is in seconds and applies to the bus start, not the PLC start. A 20-s value is reasonable for cold-start applications but should be reduced to 1 – 2 s in hot-swap or tool-changeover cells.
• Response monitoring time (QVZ) of 100 ms is tight for 187.5 kbit/s with a single ET200U. If the slave periodically fails during motor-start EMI bursts, raise the QVZ to 200 – 500 ms or fit ferrite cores on the bus cable near the slave.

FAQ