Configuring Wago 750-323 PROFIBUS on Siemens C7-633 DP GSD

1. System Overview

The SIMATIC C7-633 DP combines a S7-300-class CPU (CPU 313C-2 DP variant) with an integrated OP3 operator panel and PROFIBUS DP master interface in a single housing. The C7-633 DP exposes a 9-pin sub-D PROFIBUS DP port on the underside of the unit, electrically isolated to RS-485, capable of DP-V0 and DP-V1 services at 9.6 kbit/s to 12 Mbit/s. It is configured with STEP 7 V5.x (typically V5.5 + SPx) using the integrated HW Config tool.

The WAGO 750-323 is the PROFIBUS DP/V1 coupler for the WAGO 750 Series I/O system. It terminates the PROFIBUS segment with a 9-pin sub-D connector, isolates the fieldbus from the backplane, and supports up to 63 I/O modules per node (electrical limit 10 modules without repeater due to 5 V backplane current; module count beyond 10 typically requires a 750-622 PROFIBUS repeater or 750-325 Eco coupler). The 750-323 allocates the standard PROFIBUS diagnostic address set and supports DP-V1 extended diagnostics.

A typical configuration described here carries:

• 9 x WAGO 750-402 (4 DI, 24 VDC, type 1) = 36 digital inputs
• 6 x WAGO 750-504 (4 DO, 24 VDC, 0.5 A) = 24 digital outputs
• WAGO 750-910 configuration/commissioning tool (separate utility, not on the bus)

Inputs map to byte offsets 0..4 in the input process image; outputs map to byte offsets 0..2 in the output process image. The exact mapping depends on slot order and on whether you allow packing. The C7-633 DP can read up to 1024 DI / 1024 DO bytes via PROFIBUS DP (DP-V0 limit of 32 bytes/32 bytes per slave applies to compact diagnostics only; the 750-323 supports DP-V1, raising the useful payload to 244 bytes per slot).

2. Prerequisites

Before configuring the bus, verify the following items are present and functional:

• STEP 7 V5.5 + SP4 (or later) installed on the programming PC. HW Config must recognise the C7-633 DP under SIMATIC 300 > C7-633 DP. The hardware support package for the C7-633 DP ships with STEP 7; no HSP is normally required.
• WAGO 750-323 GSD file imported. The GSD for the 750-323 must be downloaded from the official WAGO download portal (file WAGO_750_323.gsd or revision-specific equivalent). Do not import generic PROFIBUS DP slave GSDs from third-party sites.
• WAGO 750-910 service tool or WAGO-I/O-CHECK commissioning software (for verifying node health and bus terminator on a PC basis).
• PROFIBUS DP cable with characteristic impedance 150 Ω (Siemens 6XV1830-0EH10 or equivalent). Termination ON at both physical ends only (typically at the C7-633 DP and at the last 750-323 with its terminator switches ON).
• Station addresses: C7-633 DP default master address 2; WAGO 750-323 default slave address 1 (rotary switches on the right side of the coupler, two BCD decade switches). Address must be unique on the segment.
• Online connection: PC adapter (PC USB adapter, e.g. 6ES7972-0CB20-0XA0) or MPI/DP cable connected to the C7-633 DP multi-function port.

3. Installing the WAGO 750-323 GSD File in STEP 7

The GSD file tells HW Config what the 750-323 supports: supported baud rates, diagnostic length, module catalogue entries, and I/O channel allocation. Without the correct GSD, the 4-channel WAGO modules will not appear in the HW Config catalogue.

1. Open the WAGO download portal and navigate to the 750-323 product page. Download the latest GSD revision and any associated bitmap files (BMP/DIB). Confirm the GSD file checksum if provided.
2. In STEP 7, choose Options > Install GSD File... from the HW Config menu.
3. Browse to the .GSD file and click Install. STEP 7 copies the file to ...\Siemens\Step7\S7data\GSD and the bitmaps to the BMP subdirectory.
4. After the import, refresh the hardware catalogue via Options > Update Catalogue. The WAGO 750-323 should now appear under PROFIBUS DP > I/O > WAGO > 750 Series.
5. Insert the 750-323 into the PROFIBUS subnet, then drag the appropriate modules (e.g. 750-402 4DI 24V, 750-504 4DO 24V/0.5A) into slots 1..15 of the node. The order of slots determines the byte offset in the process image.

If the WAGO 750-323 does not appear in the catalogue after the import, check the following:

• The GSD is for the 750-323 and not the older 750-322 (different DIP-switch addressing scheme).
• STEP 7 is not blocked from writing to its GSD folder (Windows UAC; run STEP 7 as administrator).
• Multiple GSD revisions are not conflicting. Remove obsolete WAGO GSDs from the ...\S7data\GSD directory before reinstalling.

4. Configuring the Wago 750-323 in HW Config

Open the properties dialog of the 750-323 and set the station address to match the rotary switches on the physical coupler. Recommended PROFIBUS parameters for the 750-323 on a DP-V1 segment:

For each I/O module slot, choose the matching 4-channel module entry. Avoid mixing 2-channel, 4-channel, and 8-channel entries unless you also use WAGO's "compact" module entries that pack multiple slots into one PROFIBUS slot. The standard 1:1 mapping is simpler and is the recommended first configuration.

5. Uploading the Hardware Configuration to the C7-633 DP

The phrase "uploading the station" in STEP 7 has two distinct meanings:

• Download (PC > C7-633 DP): HW Config > PLC > Download to Target System. Writes the configured hardware to the CPU's SDBs (System Data Blocks).
• Upload (C7-633 DP > PC): HW Config > PLC > Upload Station to PG. Reads the current SDB configuration from the connected CPU.

To check whether the online CPU configuration matches the offline project, perform an Upload Station to PG. This is the correct procedure when the machine wiring has been changed or when an offline project differs from the running machine. The uploaded configuration reflects what the CPU is using to drive PROFIBUS, including:

• Configured DP slaves and their addresses
• Module slot assignments
• I/O address ranges
• Diagnostic addresses (where relevant)

If the WAGO 750-323 is configured online but the 4 DI/DO modules do not appear in the online view, the CPU has the wrong SDB. Compare the offline project with the uploaded station; mismatches usually point to a missing GSD file or a slot that was added after the last download.

6. Reading the Process Image and Output Diagnostics

The output LEDs on the 750-323 and on each 750-504 module illuminate when the module's physical output driver is energised. Lit output LEDs therefore confirm one of the following:

1. The CPU is writing a logic 1 to the output bit (the most common case when the field wiring is correct).
2. The output module is latched via fail-safe behaviour (not applicable to 750-504 standard outputs).
3. The output driver has failed short (rare; the LED remains on regardless of the CPU state).

To verify whether the CPU is driving the outputs, use the following procedure:

1. Open a STEP 7 online connection to the C7-633 DP.
2. Open Monitor/Modify from the program editor or from a VAT table (Variable Table).
3. Enter the output byte addresses. For 6 x 750-504 modules at slot offsets 1..6, the output byte range is typically IB0..IB2 (PIB 0..2) when packed, or QB0..QB5 when not packed. The exact mapping is visible in HW Config under the slave properties.
4. Force or modify the output bits and observe the actuator response. If the actuator does not respond but the 750-504 output LED is on, suspect a field-wiring issue (open conductor, failed contactor coil, blown fuse, or wrong voltage).

The input process image (PI) is checked the same way: open a VAT table over the input bytes and toggle field devices manually while observing the bit transitions.

7. Interpreting LED Status Indicators

The WAGO 750-323 front panel has six status LEDs. Each LED indicates one bus or module condition:

Reported status: BF OFF and outputs lit. This combination is consistent with normal PROFIBUS communication. The C7-633 DP master is exchanging data with the 750-323 slave without diagnostics. The "machine not responding" symptom is therefore not a PROFIBUS-layer fault but a logic-layer or field-wiring issue.

8. Root-Cause Analysis: Machine Not Responding

Given that the BF LED is off, the most likely root causes, in order of probability:

1. CPU is in STOP. The C7-633 DP places outputs into the configured substitute value (default 0) when in STOP, but DP slaves continue to operate. The 750-504 outputs latch off because the master output bytes are 0.
2. Wrong output addresses in the user program. The user program writes to byte addresses that do not correspond to the configured PROFIBUS slot mapping. Verify the addresses used in the program against HW Config.
3. Substitute value strategy active. With "Output Substitute Value" enabled, DP failure trips outputs even when the bus is healthy. Disable the substitute value on a healthy segment if continuous output is required.
4. Failed output module. One or more 750-504 modules has a failed driver. Check each module's output LEDs individually and cross-reference with the corresponding actuator.
5. Field wiring fault. Cable break, blown fuse, contactor coil open, or 24 V supply missing at the actuator. Use the 750-910 service tool to read each module's input voltage and channel diagnostics.
6. CPU logic error. The user program never reaches the motion block because of an unfulfilled interlock (limit switch, safety relay, enable bit). Check the input process image first; if the relevant input bit is not true, the actuator will not run.

9. Using the WAGO 750-910 Service Tool

The 750-910 is a hand-held service tool that plugs into the service port of any 750 Series coupler. It is the fastest way to verify module health on a suspected node:

1. Power off the bus terminator before connecting the 750-910, or use the service port which does not require bus termination.
2. Power on the coupler. The 750-910 lists each module in slot order, reporting module type, serial number, and diagnostic state.
3. Any module reported in red or with a non-zero diagnostic code should be replaced.
4. Use the tool's I/O test mode to drive each output manually and confirm field response, isolating field-wiring faults from configuration faults.

10. Troubleshooting Matrix

11. Verification and Acceptance Test

After configuration and download, perform the following acceptance test before releasing the machine to production:

1. Cycle power on the bus and the C7-633 DP. Confirm all 750 Series LEDs reach the healthy state within 5 seconds.
2. In a VAT table, force each output bit individually. Confirm actuator response and field device state.
3. Manually actuate each input device. Confirm the corresponding input bit transitions in the VAT table.
4. Remove the PROFIBUS cable at the 750-323. Confirm BF lights, SF lights if configured, and outputs follow the substitute value strategy (0 by default).
5. Restore the cable. Confirm automatic reconnection without CPU restart, and outputs return to commanded state.
6. Save the STEP 7 project (with GSD file references) to the engineering archive and export the SDBs as part of the project backup.

12. Field-Proven Caveats

Three issues recur in C7-633 DP + WAGO 750-323 installations:

• CPU 313C-2 derivative, not full S7-300. The C7-633 DP ships a CPU 313C-2-derived CPU with reduced work memory. Large user programs that exceed 64 KByte of MC7 code will fail to load. If the project is near the limit, consider migrating to a CPU 315-2 DP or a C7-635 / C7-636.
• Watchdog time too short. The default PROFIBUS watchdog is 10 s. If the segment is occasionally interrupted during routing of cables through machinery, increase the watchdog or the Tslot values in the slave properties to avoid nuisance station failures.
• WAGO field supply jumper contacts. Each 750 Series module carries a power jumper contact. If the 24 V field supply is missing on the leftmost module, downstream modules will not energise outputs even if the system supply LED is green. Verify the 24 V field supply at every module using the 750-910 service tool.

FAQ