Overview
The Siemens order numbers 6ES7870-1AA01-0YA0 and 6ES7870-1AA01-0YA1 are the two production variants of the SIMATIC S7 Modbus Master V3.1 single license. They authorize Modbus RTU and Modbus ASCII master functionality on the CP341 and CP441-2 communication processors when an S7-300 station acts as the master on a serial Modbus network. The licensed binary is identical between the two releases; the only delta is the delivery media. The -0YA0 variant ships a CD containing the Modbus Master V3.1 installation software and the printed/PDF documentation, while the -0YA1 variant ships only the hardware license dongle. In both cases, the customer is still required to obtain the install media (typically by download from Siemens Industry Online Support) before commissioning.
Selecting between the two is therefore a procurement decision driven by media policy, not by feature or compatibility. The remainder of this reference explains the hardware context that the license protects, the exact ordering-data breakdown, the STEP 7 V4.2 and TIA Portal integration paths, the dongle mechanics, the field installation procedure, and the migration considerations that typically surface when a long-running S7-300 fleet is upgraded or re-licensed.
Hardware Context: CP341 and CP441-2 Communication Processors
The license under both part numbers is a loadable driver, not a physical module. It activates protocol firmware inside two specific Siemens point-to-point communication processors that plug into the S7-300 backplane:
| Module | Order number (representative) | Channels | Role in this license |
|---|---|---|---|
| CP341 | 6ES7341-1CH02-0AE0 (RS485/RS422), 6ES7341-1AH02-0AE0 (RS232), 6ES7341-1BH02-0AE0 (20 mA TTY) | 1 serial channel | Reference HW for Modbus Master V3.1 |
| CP441-2 | 6ES7441-2AA02-0AE0 base module, plus 6ES7441-1AA02-0AE0 / -2AE0 inserts | Up to 2 serial inserts per base | Reference HW for Modbus Master V3.1 |
Both modules are loaded with a base point-to-point firmware at delivery. Modbus master functionality is unlocked only after the licensed Modbus Master V3.1 driver has been transferred to the module through STEP 7 or TIA Portal. Without a valid license dongle attached at runtime, the CP refuses Modbus frames and reports a licensing fault on the diagnostic buffer (typical entries No valid license for Modbus driver).
Because the dongle must be present on the programming device or PC that performs the driver download, or on the CP itself depending on the binding mode, the question of which dongle type was supplied with the original package is operationally important and is covered in the licensing section below.
Ordering Data Breakdown
The Siemens product data sheet string for both variants is reproduced here verbatim from the catalog. Differences are highlighted.
| Field | 6ES7870-1AA01-0YA0 | 6ES7870-1AA01-0YA1 |
|---|---|---|
| Product family | SIMATIC S7 | SIMATIC S7 |
| Function | MODBUS MASTER V3.1 SINGLE LICENSE F.1 INSTALLATION R-SW | MODBUS MASTER V3.1 SINGLE LICENSE F.1 INSTALLATION R-SW |
| Delivery medium | SW AND DOCU. ON CD | WITHOUT SW AND DOCU. |
| License enforcement | HW-DONGLE | HW-DONGLE |
| License class | Class A | Class A |
| Languages | G, E, F (3) | G, E, F (3) |
| Executable under | STEP 7 from V4.2 | STEP 7 from V4.2 |
| Reference hardware | CP341 and CP441-2 | CP341 and CP441-2 |
| Typical procurement use | Brownfield, spare-parts replacement, sites with strict offline media requirements | New installations, sites that already maintain a Siemens download entitlement |
The functional license key, the binding to the dongle, and the supported STEP 7 versions are unchanged. From a controller perspective the two license packages behave identically once the driver is loaded.
License Comparison Matrix
The following matrix is the at-a-glance reference for the selection question raised in the original engineering thread.
| Attribute | -0YA0 | -0YA1 | Engineer implication |
|---|---|---|---|
| Modbus Master version | 3.1 | 3.1 | Identical feature set on CP341 / CP441-2 |
| STEP 7 minimum | V4.2 | V4.2 | STEP 7 V5.x is supported; Classic environment only |
| TIA Portal | Via dedicated entry 99742134 | Via dedicated entry 99742134 | Neither ships a TIA Portal HSP by default; integration is documented in the support entry |
| CP341 support | Yes | Yes | Both -1AH02 / -1BH02 / -1CH02 variants |
| CP441-2 support | Yes | Yes | Requires CP441-2 base + serial insert |
| Number of languages | 3 (de/en/fr) | 3 (de/en/fr) | No impact on functionality |
| Dongle type | Hardware dongle | Hardware dongle | License is not a soft-key / no CoL transfer without dongle swap |
| Documentation media | Included on CD | Not included | Download separately if a paper/PDF copy is needed |
| Install media | Included on CD | Not included | Must be sourced from Siemens Industry Online Support or an existing customer DVD set |
| Single license scope | One engineering seat / one runtime binding per dongle | Same | For multi-station fleets, order one license per dongle/CPU pair |
Software Stack and STEP 7 Integration
Both packages authorize the same Modbus Master V3.1 driver to be loaded through STEP 7 V4.2 or later (typically STEP 7 V5.4 / V5.5 in modern brownfield deployments). The integration steps at the engineering station are:
- Install SIMATIC STEP 7 from a separately purchased or already present STEP 7 media kit. The Modbus Master driver is not bundled with STEP 7; it is a separate installation that registers as an option package (OP) inside the STEP 7 hardware catalog.
- Run the Modbus_Master_V3.1 setup. The installer prompts for the dongle to be attached so that the license can be verified locally.
- Restart STEP 7. The CP341 and CP441-2 appear in HW Config with a Modbus Master protocol selection under the module's protocol tab.
- Configure the Modbus master port: RTU vs ASCII, baud rate (typically 1200 to 19200 for legacy Modbus RTU slaves, up to 115200 on the CP441-2), parity, slave addresses, and the FB/FC mapping.
- Download the project, including the Modbus driver block, to the S7-300 CPU. The CP retains the licensed driver in flash and continues to function without the dongle after the initial download, provided the dongle is bound to the CP rather than to the engineering station.
STEP 7 V4.2 is the stated minimum. Practical field experience shows that STEP 7 V5.4 SP5 or later is recommended because of several historical issues with the Modbus driver on the CP441-2 base insert when used with very early service packs.
TIA Portal Integration Path
The Modbus Master V3.1 driver was originally released against STEP 7 Classic and is not a native TIA Portal HSP. However, integration into TIA Portal is documented in Siemens support entry ID 99742134, available at Siemens Support Entry 99742134. That entry explains how to install the Modbus Master V3.1 driver as a TIA Portal option and how to use it on the CP341 / CP441-2 inside a TIA project.
When working in TIA Portal the following practical constraints apply:
- The CP341 and CP441-2 are supported as S7-300 communication modules in TIA Portal but only with a TIA-compatible HSP. Confirm that the installed HSP is current, otherwise the modules may not appear in the device catalog.
- The Modbus Master V3.1 option package registers a sub-protocol under the CP's properties. The setup dialog has the same fields as in STEP 7 Classic (mode, baud, parity, slave address, FB assignment).
- The license dongle check is identical: the dongle must be present at the engineering station during driver install and during any per-CP license transfer.
- Projects that mix STEP 7 Classic and TIA Portal are not natively supported; pick one toolchain per CPU to avoid configuration drift.
For greenfield TIA Portal work, consider whether a CP341/CP441-2 with the Modbus Master V3.1 driver is still the optimal architecture. Newer S7-1500 / ET 200SP communication modules often provide Modbus master support natively without a separately licensed driver. The CP341/CP441-2 path remains the correct choice when the existing fleet, the existing wiring, or the existing slave devices dictate the platform.
Licensing and Dongle Mechanics
Both variants ship with a hardware dongle. The dongle is the legal license container; the CD (in -0YA0) or the downloaded media (with -0YA1) is the install payload. The dongle carries a Siemens license key that is checked at install time and optionally transferred to a CP at commissioning time.
| Dongle characteristic | Value | Notes |
|---|---|---|
| Type | Hardware (HASP / CodeMeter-class) | Not a software license; cannot be moved without the physical token |
| Form factor (historical) | Parallel port or USB | USB is the modern default; parallel-port dongles are obsolete on current PCs |
| License class | Class A | Single seat / single binding |
| Binding target | Engineering PC or CP serial number | Set during driver setup |
| Replaceable on failure | Yes, via Siemens license reissue | Requires original proof of purchase and the failed dongle's serial number |
Field-proven caveats:
- USB dongles are sensitive to interruption during the initial license transfer. Always perform the transfer with a UPS-backed engineering laptop and avoid docking stations with aggressive USB power management.
- If the dongle is lost, Siemens can reissue the license against a new dongle but only after the original dongle has been formally de-registered. Expect paperwork; budget for it in advance.
- The license key on the dongle does not re-validate at runtime once it has been transferred to a CP. The CP then enforces Modbus master behavior based on its own stored key. This is what makes "dongle-less" operation possible after commissioning.
Installation and Commissioning Procedure
Use the following sequence as a field checklist when commissioning a new CP341 or CP441-2 with a 6ES7870-1AA01 license, regardless of whether the install media was supplied on CD (-0YA0) or downloaded separately (-0YA1).
- Verify prerequisites. STEP 7 V4.2 or later (or TIA Portal with entry 99742134 installed). Administrator rights on the engineering PC. HW dongle present and recognized.
- Install the driver. Run the Modbus Master V3.1 setup. If using -0YA1, point the installer at the extracted downloaded image. If using -0YA0, the installer is on the bundled CD.
- Restart STEP 7 / TIA Portal. Confirm that the CP341 and CP441-2 now expose the Modbus Master protocol option.
- HW Config. Place the CP in the S7-300 rack (slot 4 to 11 for CP341 in slot-rule-compliant positions). For CP441-2, place the base insert in a suitable slot and add the serial sub-insert.
- Protocol parameters. Set mode (RTU/ASCII), baud, parity, response timeout (typical 1000 ms for RTU, longer for slow slaves), inter-frame delay, and the Modbus master function code mapping (FC01/02/03/04/05/06/15/16).
- FB integration. Map the Modbus driver FBs (FB7 / FB8 for CP341 in Classic; equivalent blocks for CP441-2) into the S7 program. Provide instance DBs for each slave.
- Download and bind. Download the hardware configuration and the program. The driver prompts to transfer the license from the dongle to the CP. Confirm the CP serial number matches.
- Verification. Use the diagnostic buffer of the CP to confirm that the Modbus driver loaded successfully and that no license fault is reported. Run a single-slave read test (FC03 holding register) and verify with the slave's own diagnostic tooling.
Migration from -0YA0 to -0YA1
Many long-running S7-300 fleets are mid-life when the -0YA0 stock is exhausted and only -0YA1 is available. The migration is straightforward when the existing installation is healthy:
- Source the Modbus Master V3.1 install media from Siemens Industry Online Support if you do not already have an image in your engineering image library.
- Order the -0YA1 license to obtain a hardware dongle.
- Bind the new dongle to the existing CP serial numbers during the next maintenance window. The binding is per-CP and does not require a project re-download.
- Update the spare-parts inventory records to reflect the new part number.
If the existing CP licenses were bound to an engineering PC rather than to a CP, the dongle swap requires that PC to be re-authorized. Schedule a one-hour engineering outage.
Selection Decision Guide
Use the following checklist to choose between the two part numbers in a given procurement context:
- Choose 6ES7870-1AA01-0YA0 when: the site policy mandates that install media be supplied with the license on physical media, the engineer cannot rely on Siemens download access (air-gapped networks, restricted procurement), or the spare is replacing a missing CD in an existing install.
- Choose 6ES7870-1AA01-0YA1 when: the organization already maintains a Siemens download entitlement, the receiving site is connected and can fetch the install image, the customer wants to minimize the number of moving parts (no obsolete CDs), or the older -0YA0 stock has been discontinued and only -0YA1 is orderable.
Functionally the two are interchangeable once installed.
Troubleshooting Matrix
| Symptom | Likely cause | Resolution |
|---|---|---|
| CP does not list Modbus Master as a protocol option in HW Config | Modbus Master V3.1 driver not installed, or installed against a different STEP 7 version | Reinstall the option package matching the STEP 7 version in use; verify the OP appears in the installed options dialog |
| Diagnostic buffer reports license fault after driver download | Dongle not present, dongle driver (HASP runtime) not installed, or dongle bound to a different PC | Install the HASP runtime; reinsert the dongle; re-bind the license to the current PC or transfer to CP |
| Modbus master loads but no slave response | Wrong slave address, wrong parity/baud, swapped RS485 A/B, missing termination | Validate parameters with a Modbus scanner on the same cable; confirm polarity; install termination at both ends of the RS485 bus |
| Intermittent CRC errors on RTU | Inter-frame delay too short, baud too high for the cable length, electrical noise | Increase inter-frame delay to 3.5 character times; lower baud; check shield grounding |
| CP441-2 base insert not recognized | Firmware mismatch with insert, missing HSP update | Update the HSP for CP441-2 in TIA Portal / HW Config; cross-check insert compatibility |
| Dongle lost after binding to PC | Hardware failure or loss | Contact Siemens license support with the original dongle serial number and proof of purchase to reissue |
FAQ
What is the actual difference between 6ES7870-1AA01-0YA0 and 6ES7870-1AA01-0YA1?
Only the delivery media. Both part numbers are the SIMATIC S7 Modbus Master V3.1 single license for CP341 and CP441-2, Class A, 3 languages, with a hardware dongle, executable under STEP 7 from V4.2. The -0YA0 ships software and documentation on CD; the -0YA1 ships only the dongle and the install media must be obtained separately from Siemens Industry Online Support.
Does the -0YA1 license work in TIA Portal?
Yes, the same driver is supported in TIA Portal via the procedure documented in Siemens Support Entry 99742134. Both part numbers behave identically once installed; the TIA Portal integration does not depend on whether the install media arrived on CD or as a download.
Can I use one license on multiple CP341 modules in the same project?
No. The single license (Class A) authorizes one engineering seat and one runtime binding. To cover multiple CP341 or CP441-2 modules, order one license per dongle/CPU pair. The license is bound to a specific CP serial number during commissioning, after which the dongle can be removed.
Is STEP 7 V4.2 still a realistic minimum in 2025+ deployments?
STEP 7 V4.2 is the published minimum for the Modbus Master V3.1 driver, but in practice STEP 7 V5.4 SP5 or STEP 7 V5.5 is recommended for current installations. TIA Portal users should rely on the integration path documented in Siemens Support Entry 99742134 and ensure the matching HSP for CP341/CP441-2 is installed.
What happens if the hardware dongle is lost?
Siemens can reissue the license against a new dongle provided the original dongle serial number and proof of purchase are available, and provided the lost dongle can be de-registered. Budget time for this process and consider keeping a second license on the shelf as a contingency for critical S7-300 fleets.