Product Overview
The Siemens 6ES7870-1AA01-0YA0 is not a hardware module but a SIMATIC S7 MODBUS Master V3.1 software authorization kit—comprising a CD carrying the loadable driver, STEP 7 function blocks, and multilingual documentation, plus a Class-A hardware dongle that unlocks Modbus RTU master capability on S7-300 and S7-400 racks equipped with a CP 341 or CP 441-2 point-to-point serial communication processor. Within the Siemens automation software hierarchy, the Siemens 6ES7870-1AA01-0YA0 sits in the “loadable drivers for CP 441-2 and CP 341” family (ST79-SW catalog group), and its job is to turn a bare CP 341/CP441-2—which natively supports only ASCII, 3964R, and RK512—into a fully capable Modbus RTU master that can poll 1–247 slaves across RS485 half-duplex, RS422, RS232, or TTY physical layers. The single-installation runtime license is dongle-bound: the Siemens 6ES7870-1AA01-0YA0 dongle plugs into the programming PC, and STEP 7 V4.02 or higher (SIMATIC Manager era; TIA Portal requires STEP 7 V5.x compatible-mode project) is the minimum software environment.
Positioning-wise, the Siemens 6ES7870-1AA01-0YA0 solves a very specific legacy-integration problem: thousands of S7-300 (CPU313/314/315/316/317) and S7-400 (CPU414/416/417) panels commissioned in the 1998–2010 window still run CP 341 or CP 441-2 cards for serial comms, and the plant needs to talk Modbus RTU to third-party VFDs, power meters, temperature controllers, flow transmitters, and SCADA-fronted instruments that never got a PROFIBUS or PROFINET face-lift. Writing a Modbus RTU stack from scratch on an S7-400 STL is possible but wasteful; the Siemens 6ES7870-1AA01-0YA0 hands the engineer a vendor-certified FB/FC library that encapsulates CRC generation, inter-frame timing, slave timeout, and retry logic, turning a multi-day coding job into a half-day configuration task. The Siemens 6ES7870-1AA01-0YA0 is the original V3.1 release (0YA0 suffix); Siemens later released 6ES7870-1AA01-0YA1 as the refreshed kit with updated driver and broader STEP 7 compatibility, but the 0YA0 remains in active PLM status and is still the specified spare on many as-maintained BOMs. One practical nuance worth stating upfront: the CP 341 slave function is free (built into the CP firmware); the Siemens 6ES7870-1AA01-0YA0 dongle is only required for the master role. Many first-time buyers confuse the two.
Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | 6ES7870-1AA01-0YA0 |
| Manufacturer | Siemens |
| Product Type | Communication Software Package / Loadable Driver (MODBUS Master) |
| Software Version | V3.1 |
| License Type | Single license, 1 installation (R-SW) |
| Reference Hardware | CP 341 (S7-300), CP 441-2 (S7-400); optionally CP 340/CP 440 referenced in broader field use |
| Protocol | Modbus RTU only (Master mode); no Modbus ASCII, no Modbus TCP |
| Supported Function Codes | 01, 02, 03, 04, 05, 06, 15, 16, 22, 23 |
| Slave Address Range | 1 – 247 |
| Baud Rate | 300 – 76,800 bps (TTY interface capped at 19,200 bps) |
| Bus Topology | RS485 half-duplex multi-drop, up to 32 slaves per segment typical |
| Media / Delivery | Software & documentation on CD, HW dongle (USB-type authorization) |
| Programming Environment | STEP 7 V4.02 or higher (SIMATIC Manager); TIA Portal requires STEP 7 V5.x compatible project mode |
| Documentation Languages | 3 languages: German, French, English |
| Classification | Class A |
| Net Weight | 0.203 kg (pkg) |
| EAN / UPC | 4019169009331 / 662643174755 |
| Lifecycle (PLM) | PM300 Active Product (spare/maintenance stream) |
| Successor Reference | 6ES7870-1AA01-0YA1 (refreshed V3.1 kit) |
Main Features and Advantages
The Siemens 6ES7870-1AA01-0YA0 distinguishes itself not through flashy UI but through the unglamorous work of wrapping a fragile serial protocol into a rock-stable FB call that S7-300/400 veterans trust on live process racks. The headline feature is the encapsulated Modbus RTU master stack: CRC-16 calculation, inter-character and inter-frame silence timing (3.5-character rule), slave-response timeout, and automatic retry are all buried inside the Siemens-supplied FB/FC blocks, so the application engineer configures a data-exchange DB—target slave address, function code, starting register, word count—and the Siemens 6ES7870-1AA01-0YA0 driver handles the wire-level framing. This alone converts what would be three days of STL/SCL debugging into a morning of DB-filling, and more importantly, the vendor-certified stack survives electrical noise on RS485 that a home-rolled LAD implementation would choke on.
Hardware flexibility around the CP 341 / CP 441-2 pairing is the second pillar. The Siemens 6ES7870-1AA01-0YA0 loadable driver attaches to whichever physical interface the CP is ordered with—RS232 (short-run config-panel comms), RS422 (full-duplex point-to-point), RS485 (the default for multi-drop RTU bus to 32 slaves), or TTY (legacy Siemens peripheral, baud capped at 19.2 k on the Siemens 6ES7870-1AA01-0YA0‘s TTY path). A single S7-400 rack with two CP 441-2 cards can run two independent Modbus RTU masters—say, one polling a turbine-generator’s power-quality meter string, the other talking to a boiler-field VFD bank—while the CPU’s MPI/PROFIBUS side handles the HMI and upstream OS. The Siemens 6ES7870-1AA01-0YA0 driver scales to the CPU’s scan-cycle budget; practically, 32–64 slaves per CP is comfortable on a 300-class CPU, pushing higher on a 400-class if the poll spacing is tuned.
Dongle-based licensing deserves its own comment because it shapes how plants manage the Siemens 6ES7870-1AA01-0YA0. The HW dongle plugs into the programming PC, not into the PLC rack—licensing is development-time, not runtime. Once the FB blocks are compiled, downloaded, and the CP loaded with the driver, the PLC executes the Modbus master loop without the dongle present. The dongle only needs to be re-inserted when the project is reopened in STEP 7 for edits/re-download. For maintenance teams where the “project laptop” is a shared resource, this means the Siemens 6ES7870-1AA01-0YA0 dongle lives in the laptop bag (or the plant’s key-lock cabinet) alongside the S7-300/400 memory cards. Swapping to a new programming PC? Bring the dongle. Losing it? The STEP 7 project won’t reopen the Modbus FB source without it—plan spare-dongle discipline early.
A final point that saves confusion: the CP 341 Modbus slave is free (Siemens includes it in the CP firmware loadables at no extra charge). Only master needs the Siemens 6ES7870-1AA01-0YA0 dongle. Plenty of panels are wired the other way—S7-400 as slave to a DCS or SCADA via CP 341—and those never needed this SKU. If your BOM lists the Siemens 6ES7870-1AA01-0YA0, double-check you’re actually the master on that RS485 segment before ordering.