Integrating Third-Party AS-i Slaves with S7-1200 CM 1243-2

Overview: Why AS-Interface Mixes Vendor Devices Natively

AS-Interface (AS-i) is a single-master, two-wire, bit-serial fieldbus standardized in IEC 62026-2. Unlike PROFIBUS or PROFINET, AS-i does not use a GSD or GSDML file to describe a slave. Every AS-i slave carries its own identity directly on the device: a 4-nibble profile (IO, ID, ID1, ID2) plus a 5-bit address (standard) or 6-bit address (A/B extended). This means a third-party device from Festo, Aventics (formerly Bosch Rexroth), IFM, Balluff, Pepperl+Fuchs, Sick, or Turck is electrically and logically compatible with any AS-i master — including the Siemens CM 1243-2 — without firmware adaptation or vendor-specific catalog entries. The TIA Portal approach is to drop a "Universal Slave" into the device configuration, key in the profile codes from the device datasheet, and let the master expose the bits to the S7-1200 process image.

This reference walks through the CM 1243-2 (article number 6GK7243-2AX30-0XE0, firmware V2.x and later), covers both standard and A/B addressing, and shows the exact steps for a 4DI/4DO third-party valve terminal such as the Bosch Rexroth / Aventics CA44 (material number R412004452) and the Festo CPV14-VI / CPV-ASI-4E3A-Z.

Prerequisites

• SIMATIC S7-1200 CPU, firmware V4.2 or later (required for full CM 1243-2 V2.x support). S7-1200 V4.0/4.1 supports CM 1243-2 V1.0 with reduced slave count.
• CM 1243-2 AS-i master module (6GK7243-2AX30-0XE0). Slot mounted to the left of the CPU.
• AS-i power supply, 24 V DC / min 2.6 A per segment (e.g. Siemens 3RX9501-0BA00 or Phoenix Contact QUINT-PS-100).
• Yellow AS-i profile cable (EPDM, 2 x 1.5 mm²).
• AS-i addressing unit (Siemens 3RK1904-2AB02 handheld or IFM AC1224) to set the slave address on third-party devices that do not support auto-address.
• TIA Portal V15.1 or later (V16+ recommended for CM 1243-2 V2.1). The Hardware Support Package (HSP) for the CM 1243-2 must be installed.
• Manufacturer datasheet for every third-party slave — the IO, ID, ID1, ID2 profile codes MUST come from the device manual, not from a TIA Portal wizard.

CM 1243-2 Master Module Specifications

The CM 1243-2 occupies 16 bytes of input process image and 16 bytes of output process image in the S7-1200 by default, and exposes per-slave bit areas in extended configuration. Inputs from each slave are bit-mapped starting at IB 0 / QB 0 offset within the master; the offset is calculated as (slave_index × 4 bits) when working in standard profile mode, or (slave_index × 4 bits) per A/B sub-address in extended mode.

AS-i Slave Addressing: Standard (1–31) vs. A/B Extended (1A–31A, 1B–31B)

AS-i has two addressing schemes on the same physical wire:

Mixing rule: The CM 1243-2 fully supports mixed standard and A/B slaves on the same network. A standard slave at address 7 and an A/B slave at 1A/1B coexist without configuration changes to the master. The "automatic A/B addressing" checkbox in TIA Portal (under CM 1243-2 properties > AS-i network > Operating mode) must be enabled if the segment is to include any A/B slaves; otherwise the master rejects A/B slaves during configuration and logs fault 0xC (configuration error) per slave.

The AS-i Slave Profile: IO, ID, ID1, ID2 in Hex

Every AS-i slave exposes four 4-bit codes that fully describe its I/O capability to the master. These are burned into the slave at the factory and read out by the master during configuration:

The IO code is the only one that the master uses for I/O mapping. ID/ID1/ID2 are used for slave acceptance: by default the CM 1243-2 accepts any slave whose ID = F (free). For slaves with a locked ID, the master must be told the expected ID code in the device configuration, otherwise it flags a configuration error.

For a 4DI/4DO module, the most common IO codes are:

• IO = 7 (binary 0111): 4 DI + 4 DO — used by Festo CPV-ASI-4E3A-Z default profile and most general-purpose 4DI/4DO blocks.
• IO = 0 (binary 0000): 4 DI + 0 DO (input-only module).
• IO = 8 (binary 1000): 4 DI + 4 DO, alternate encoding (used by some Aventics / Rexroth CA-series valve islands).

Step-by-Step: Adding a Third-Party AS-i Slave in TIA Portal

1. Add the CM 1243-2 master. In the TIA Portal project tree, open Devices & networks, drag the CM 1243-2 (6GK7243-2AX30-0XE0) from the Hardware Catalog onto the S7-1200 left-bus slot. Assign it to the PLC via "Not connected > PLC_1" and select CM 1243-2 as the IO device.
2. Set the AS-i operating mode. Select the CM 1243-2 in the device view, open Properties > AS-i network > Operating mode. Enable AS-i specification V3.0 and check Automatic A/B addressing permitted if any A/B slaves will be on the segment.
3. Add the universal slave placeholder. In the network view, drag a new device from: Hardware Catalog > Field devices > AS-Interface > Universal slave > AS-i Standard Slave Universal (use the A/B variant if the third-party device is an A/B slave). Drop it onto the CM 1243-2 AS-i subnet.
4. Assign the AS-i address. Select the new universal slave, go to Properties > AS-i address. Enter the actual slave address as configured physically on the device (via the addressing unit, e.g. 7, or 1A/1B for A/B). The address MUST match what is on the physical device — a mismatch causes configuration error 0xC.
5. Enter the IO/ID/ID2/ID1 profile codes. Open Properties > Profile. Four fields appear: IO, ID, ID2, ID1. Enter the hex values from the manufacturer datasheet. Example for Festo CPV-ASI-4E3A-Z default configuration: IO = 7, ID = A, ID2 = E, ID1 = 7.
6. Map I/O to the S7-1200 process image. The CM 1243-2 automatically assigns input byte / output byte offsets based on the slave's position in the AS-i cycle. In the slave's Properties > I/O addresses, the start addresses are populated by TIA Portal (e.g. slave 7 → I0.0 to I0.3, Q0.0 to Q0.3 in standard mode). Reference these bits directly in the user program with %I0.0 or symbolic tags.
7. Download and verify. Compile the project, download the hardware configuration to the S7-1200, and switch the CM 1243-2 to Configuration mode via the master properties or the AS-i SET button. The master scans the network, detects the new slave, and switches to Protected operation once all configured slaves are present.

Mapping a 4DI/4DO Third-Party Slave (Worked Example: Rexroth / Aventics CA44)

The Bosch Rexroth (now Aventics) CA44 valve island (material R412004452) is a 4DI / 4DO AS-i slave. Unlike PROFIBUS or PROFINET, no GSD is required — the CA44 has the profile codes programmed in the factory. The required procedure:

1. Set the slave address on the CA44 to an unused value (1–31 for standard) using an AS-i addressing unit, e.g. address 8.
2. Power the CA44 on the AS-i yellow cable. Verify the green AS-i LED on the slave is steady (not flashing).
3. Connect TIA Portal online to the S7-1200, open Online & Diagnostics > CM 1243-2 > AS-i diagnostics > Slave list. The CA44 will appear with detected profile codes. Typical values for the CA44 are IO = 7, ID = 0, ID1 = 1, ID2 = 1 (verify in the official Aventics datasheet — part number R412004452 datasheet 100-1504-001 or successor).
4. Add the universal slave placeholder in offline configuration as described in the previous section, entering the codes recorded from the live scan.
5. Download the hardware configuration. The four inputs from the CA44 land on I-byte offsets defined by the slave position (e.g. slave 8 → I0.0 to I0.3). The four outputs (used for valve coil pilots) land on Q-byte offsets (e.g. Q0.0 to Q0.3).

Symbolic tag names in the S7-1200 user program (example for address 8):

// Inputs from CA44 (4DI)
"CA44_Input_0" AT %I0.0 : BOOL;
"CA44_Input_1" AT %I0.1 : BOOL;
"CA44_Input_2" AT %I0.2 : BOOL;
"CA44_Input_3" AT %I0.3 : BOOL;
// Outputs to CA44 (4DO - valve coils)
"CA44_Valve_1" AT %Q0.0 : BOOL;
"CA44_Valve_2" AT %Q0.1 : BOOL;
"CA44_Valve_3" AT %Q0.2 : BOOL;
"CA44_Valve_4" AT %Q0.3 : BOOL;

Worked Example: Festo CPV-ASI-4E3A-Z (A/B Slave)

The Festo CPV14-VI valve terminal with AS-i connection module CPV-ASI-4E3A-Z is a pure A/B slave. Default profile per the Festo CPV manual (page 12):

Because the ID is locked to A (not the default F), the CM 1243-2 must be configured with the expected ID code, otherwise the master flags the slave as "ID code not equal" and the slave is not accepted into the configuration. The CPV terminal also occupies two AS-i addresses (e.g. 1A and 1B) to expose 8 outputs for 4 valves. Configure both A and B sub-addresses in TIA Portal with the same IO/ID profile values.

Commissioning and Online Diagnostics

After download, the CM 1243-2 goes through the following states (visible on the front-panel LEDs and in TIA Portal):

Useful diagnostic paths in TIA Portal Online & Diagnostics for the CM 1243-2:

• Diagnostics > AS-i diagnostics > Slave list — live profile read of every detected slave
• Diagnostics > AS-i diagnostics > Configuration errors — lists slaves with code 0xC errors
• Diagnostics > AS-i diagnostics > Periphery errors — flags slaves with I/O faults
• Web server (port 80, default 192.168.0.100) — full AS-i state including cycle time, error counters, slave list, force/observe

Troubleshooting Matrix

Cross-Vendor Compatibility Notes

The CM 1243-2 (and its successor CM 1243-2 V2.1, article 6GK7243-2AX30-0XE1) interoperates with the following common third-party AS-i slaves without vendor catalog entries:

Migration Note: CM 1243-2 V1.0 vs V2.x

Older systems may have the CM 1243-2 V1.0 (6GK7243-2AX01-0XE0). The V1.0 supports AS-i Specification V2.1, which means:

• Standard slaves only (1–31). A/B slaves are NOT supported in V1.0 firmware.
• Cycle time fixed at 5 ms.
• No automatic A/B addressing.

If a third-party A/B slave must be used, replace the master with the V2.x variant (6GK7243-2AX30-0XE0) and update the TIA Portal HSP. The configuration in the project tree is identical — only the article number changes.

Standards Reference

AS-i wiring, profile codes, and master/slave behavior are defined in IEC 62026-2 and the AS-International Association "AS-i Specification V3.0". The CM 1243-2 implements V3.0 with backward compatibility to V2.1 slaves. For deeper background on the bus protocol (telegram structure, slave acceptance procedure, Manchester encoding on the yellow cable), refer to the SIMATIC NET AS-Interface — Introduction and Basics PDF, the Siemens AS-Interface product page, and the SIRIUS Act AS-Interface flyer.