How to Add HART Secondary Variables Without Shifting Other ET 200iSP I/O Addresses

You can usually preserve the addresses of other modules by assigning the ET 200iSP HART analog module a different, unused input-address range in STEP 7 HW Config instead of accepting an automatic shift of subsequent modules. The new range must fit the selected HART configuration, remain within the CPU's permitted address and process-image ranges, and overlap no other I/O. Update symbols for the moved module and verify the compiled address map before downloading.

How HART Variables Affect the Input Area

ET 200iSP analog modules with HART can map IEEE-format HART variables into the process-image input area in addition to ordinary analog values. Siemens' ET 200iSP Operating Instructions state that the HART analog modules support up to four IEEE tags and that the input image provides up to 20 bytes per module for them. The manual's I/O-byte calculation lists 4 AI/4 AO modules with HART as using up to 28 I/O bytes, compared with 8 bytes without HART. Use the module's configured address length shown by HW Config for the actual selection; do not reserve only the original analog-value bytes when the HART mapping increases the module's range.

When a Separate Address Range Helps

STEP 7 assigns module start addresses automatically, but the STEP 7 hardware-configuration manual documents changing a module's start address on its Addresses tab when free address assignment is supported. A DP-slave module is among the configurations for which STEP 7 permits this. Moving only the HART module into a free range can keep the unchanged modules at their existing addresses, avoiding a cascade of address changes. It does not make the addresses of the moved card itself stay the same: any absolute-address symbols or logic tied to that card's old locations must be checked and updated.

Method: Move the HART Module to a Free Range

Save and back up the PCS 7 project. Record the existing I/O address map and identify which symbols and CFC connections refer to the HART module and to downstream modules.
In STEP 7 HW Config, select the ET 200iSP HART analog module and open its object properties.
On the Addresses tab, inspect the current start address and address length. Determine the actual length after enabling the required number of HART variables; the module manual gives a maximum of 28 I/O bytes for a HART 4 AI/4 AO module.
Choose a start address in an unused input range large enough for the complete configured module range. Confirm that it does not overlap other inputs, reserved system/diagnostic addresses, or a range used by another DP device, and that the CPU supports the assignment.
Apply the new start address and inspect View > Address Overview. Confirm that the moved module occupies the intended range and that the other modules retain their previous addresses.
Review the symbol table and CFC connections for the moved module. Keep existing symbols for unaffected modules unchanged; update symbols for the HART card to match its new addresses and the configured HART variable mapping.
Save and compile the hardware configuration, review compile results, and follow the site-approved PCS 7 download and commissioning procedure. Verify the actual input values and HART quality/status before returning the system to service.

The menu path and address-change procedure are from the STEP 7 hardware-configuration manual. Exact available ranges and address limits depend on the CPU, process-image configuration, and existing station layout.

Addressing Considerations for HART

Each HART variable mapped into the PII uses part of the module's address range. The ET 200iSP manual says each of up to four IEEE tags occupies a five-byte block and describes assigning the selected device channel and IEEE tag to a block in the PII. Check the module parameterization and the module's resulting input length together; a range that fits the analog channels but not the HART area is not sufficient.

For projects configured with a GSD file, follow the corresponding GSD/PDM workflow and verify that the STEP 7 hardware configuration and the device parameter assignment agree. Siemens warns that GSD configuration and SIMATIC PDM parameterization must use matching slot assignments.

Preserve Symbolic References

A symbol is a name associated with an address; changing a module's start address does not automatically mean all symbolic references will follow that hardware module. Before editing, distinguish symbols and CFC connections for the moved HART module from those belonging to other cards. After changing the module address, check the symbol table, block connections and cross-references for the affected HART points, then confirm that unaffected modules still resolve to their original inputs.

Verification

In the HW Config address overview, confirm the moved module's start and end addresses and verify that the other modules have not moved. Compile the station and inspect all address and symbol diagnostics. After an approved download, compare the online hardware configuration with the intended project, then verify one ordinary analog input and each configured HART variable at the expected symbolic points, including quality/status as applicable.

Limitations and Operational Precautions

The ticket does not identify the ET 200iSP analog module order number, the S7-400 CPU model, current address map, HART variable count, process-image settings or symbol table structure. These determine the exact available range and whether free address assignment is supported. The 28 I/O bytes value is the documented maximum for the HART 4 AI/4 AO module class, not a claim that every configuration uses all 28 bytes. Hardware changes can affect the running control system; make them only under site change control with a verified backup, approved downtime and a recovery plan. Do not download a changed hardware configuration to a running process without confirming the applicable CPU and plant procedure.

Engineer FAQ

Must all module I/O addresses be consecutive? No. STEP 7 supports manual start-address assignment in applicable configurations. Each module's own address range must be contiguous and must not conflict with another assigned range.

Can I place the HART module at the end of the address map? Yes, if the chosen region is free, large enough for its configured input range, and supported by the CPU and process-image configuration.

Will moving one module renumber every module after it? Not if the other modules' start addresses are left unchanged and the chosen range is free. Verify the compiled address overview.

How many bytes should I reserve for HART values? The ET 200iSP manual allows up to four IEEE tags at five bytes each, or up to 20 bytes for tags. The HART 4 AI/4 AO module can occupy up to 28 total I/O bytes; use the exact range HW Config shows for the selected configuration.

Do the symbols automatically move with the card? Do not assume so. Review and update symbols and CFC connections for the moved card; leave symbols for unaffected modules unchanged if their addresses remain unchanged.

Where do I change a module's start address in STEP 7? The STEP 7 hardware-configuration manual documents opening the module's properties and changing its start address on the Addresses tab, when free assignment is supported.

How do I find unused addresses? Use View > Address Overview in HW Config and check the complete input/output assignment, including module ranges and reserved or diagnostic areas.

Does enabling HART variables always add 20 bytes? No. The manual specifies up to four five-byte IEEE tag blocks. The actual module range depends on the selected configuration and the resulting address length in HW Config.

Can I move this address without affecting the running process? Do not assume so. Follow the approved hardware-change and download procedure for the specific CPU and plant; schedule any required process interruption.

What must be checked after the change? Compile the hardware configuration, confirm no address overlap, verify unaffected addresses remain stable, inspect symbols for the moved card, then test each configured analog and HART value online.

Technical References

Siemens, Configuring Hardware and Communication Connections STEP 7, 05/2010, A5E02789741-01, section 2.3.9 “Assigning I/O Addresses,” pp. 47–48. Open the Siemens manual.
Siemens, ET 200iSP Operating Instructions, 12/2020, A5E00247483-AI, section 13.12.3 “Assigning the channel and IEEE tag,” pp. 323–325; Appendix A.3 I/O-byte calculation, p. 344. Open the Siemens manual.

How to Add HART Secondary Variables Without Shifting Other ET 200iSP I/O Addresses