Product Overview

The 6ES7 870-1AA01-0YA0​ is not a hardware module—it is Siemens’ MODBUS Master V3.1 loadable driver package for SIMATIC S7-300/S7-400 systems that use a CP341 or CP441-2 point-to-point communication processor to speak Modbus RTU to third-party devices. What ships in the box is a CD with the software + documentation, and a small hardware dongle that must be plugged into the back of the CP341/CP441-2 to unlock the Modbus Master firmware functions—without that dongle seated, the CP will not execute Modbus Master blocks. The 6ES7 870-1AA01-0YA0​ is the “full” SKU (SW + Doc CD + HW dongle, Class A, de/en/fr trilingual); the sibling 6ES7 870-1AA01-0YA1​ carries only the HW dongle with no CD, for sites that already have the V3.1 install media and just need a replacement key. Siemens lists the 6ES7 870-1AA01-0YA0​ as executable under STEP 7 V4.02 or higher, with the CP PtP Param (Point-to-Point Parameter Assignment) V5.1+ option package as a prerequisite—you install CP PtP first, then load the Modbus Master V3.1 driver into STEP 7’s HW Config / NetPro environment so the CP341 shows “Modbus Master” as a selectable protocol.In practice the 6ES7 870-1AA01-0YA0​ exists because Siemens S7-300/400 CPUs don’t natively do Modbus RTU—their strength is PROFIBUS/PROFINET, but plant floors are full of third-party devices (power meters, protecting relays, flow computers, VFDs, analyzers) that only speak RS-485 Modbus RTU. The CP341 (RS232 / TTY / RS422-485 variants) or CP441-2 (with an interface submodule) becomes the serial gateway, and the 6ES7 870-1AA01-0YA0​ provides the loadable firmware + STEP 7 function-block library (FB-style send/receive jobs, FC block wrappers) that lets the S7 CPU orchestrate Modbus polls to multiple slaves—典型如 S7-400H 配 CP341 连 CZAZ-UM 保护继电器，或 S7-315 + CP341 RS485 轮询十台超声波流量计。 For obsolescence buyers this is a small but critical line item: the CP341 hardware is useless for Modbus without the 6ES7 870-1AA01-0YA0​ dongle, and the dongle is easy to misplace during a cabinet rework because it sits on the back of the CP, not the front terminal strip.

Technical Specifications

Main Features and Advantages

Dongle-locked loadable firmware, one per CP.​ The 6ES7 870-1AA01-0YA0​ dongle plugs into a small slot on the rear of the CP341 or CP441-2 (not the front where the RS485 terminal sits—this trips up first-time installers). Without the dongle the CP can still run as a generic PtP serial port, but the Modbus Master protocol stack and the associated STEP 7 FB/FC blocks refuse to execute. The dongle is CP-bound, not CPU-bound—move it to another CP341 and it works there; clone it and STEP 7 will reject it. For S7-400H setups with redundant CP341 pairs, each CP needs its own 6ES7 870-1AA01-0YA0​ dongle, which is why the “single installation” phrasing on the label matters at procurement time.V3.1 function-block library for multi-slave polling.​ Installing the 6ES7 870-1AA01-0YA0​ drops a set of FB/FC blocks into the STEP 7 library—job-build blocks where you write the Modbus request (function code 03/04 read holding/input registers, 06/16 write single/multiple registers, 01/02 read coils/discrete inputs, 15 write multiple coils) into a SEND data block, set the slave address, register start, word count, and connection ID (from NetPro’s PtP connection), then trigger the FB. The CP handles the RS485 framing, CRC, retry-on-timeout, and the FB drops the response into a RECV DB. Multi-slave polling is done by cycling the slave address and register parameters in the S7 OB1/OB35—classic pattern is one FB call per slave, or one FB cycled through an index. The 6ES7 870-1AA01-0YA0​ manual (on the CD) includes a sample project in STL that most commissioning engineers copy-paste then adapt, which is why the “SW + Doc” part of the SKU matters more than it looks.RTU framing + baud/parity flexible.​ The 6ES7 870-1AA01-0YA0​ lets the CP341 be parameterized in HW Config for baud (up to 76.8 kbps on RS485, typical 9.6 k / 19.2 k / 38.4 k for plant meters), data bits (8), stop bits (1/2), parity (none/even/odd), and the usual Modbus slave timeout / inter-character gap settings. TIA Portal (V13+) also recognizes the 6ES7 870-1AA01-0YA0​ dongle—once the CP341 is in the device view, you right-click → Online & Diagnostics → Load Special Driver to push the V3.1 firmware onto the CP, then HW Config’s Protocol dropdown shows “Modbus Master” as selectable. That TIA path is newer than the classic STEP 7 V5.x PtPParam flow, but the 6ES7 870-1AA01-0YA0​ covers both.Prerequisite chain matters.​ The 6ES7 870-1AA01-0YA0​ is loadable, meaning it sits on top of the CP PtP Param driver. Install order: STEP 7 → CP PtP Param V5.1+ → 6ES7 870-1AA01-0YA0​ (insert CD, setup.exe registers the blocks + HW Config envelope + dongle certificate). Skip CP PtP and HW Config won’t show “Modbus Master” as a protocol pick under the CP341 parameters—this is the #1 support call for first-time CP341 Modbus projects. Also worth noting: CP441-2 needs an additional interface submodule (6ES7963-1AA10 RS232 / -2AA10 TTY / -3AA10 RS422-485) before the 6ES7 870-1AA01-0YA0​ dongle has anything to drive—CP441-2 alone is just a processor carrier, the physical serial port lives on the interface submodule.-0YA0 vs -0YA1 procurement choice.​ The 6ES7 870-1AA01-0YA0​ (this SKU) = CD + doc + dongle, for new projects or when the install media is lost. The 6ES7 870-1AA01-0YA1​ = dongle only, no CD, for sites that already have the V3.1 CD from a prior purchase and just need a replacement key (dongles walk off during cabinet audits—ask any S7-400H service tech). Both use the same V3.1 loadable image; the only diff is media. For spare-parts buyers, stocking -0YA1 is cheaper if the engineering laptops already hold the CD image; stocking -0YA0 is safer for new-project kits where the CD might be the only copy on site.