SINAMICS G120 PROFINET Standard FB: Create, Call in OB1 and Map to I/Q Addresses

• One FB, one instance DB per drive. A second drive needs a new call and new addresses — no new code.
• Give the "held at 1" bits a default of TRUE, so OB1 only wires what actually changes.
• Take the I and Q addresses from the Device overview of the G120, never from memory.
• Read "running" from Oper_En (ZSW1 bit 2), never from the ON_OFF1 command.

Try it first: the Live PLC–VFD Simulator runs the same telegram this block writes, so you can see the control word before you build the FB.

Why One Standard FB for Every G120

A plant with ten G120 drives can have ten copies of the same bit mapping scattered through OB1 — or one tested function block called ten times. The second approach is what "standard FB" means: the drive logic is written and verified once, and each drive only differs in its instance DB and its I/Q addresses.

This guide builds that block for Standard Telegram 1 (PZD-2/2) on an S7-1200 or S7-1500, in four steps: create the interface, write the networks, call it in OB1, and map it to the telegram's I and Q addresses. The meaning of every individual bit is covered in SINAMICS G120 STW1 and ZSW1: Every Control and Status Bit; this page focuses on the block itself.

Block Diagram: OB1, FB, I/Q Addresses and Drive

Data passes through four stages. OB1 supplies machine tags to the FB; the FB packs them into words; the words sit in the PLC's process image at the telegram's addresses; and PROFINET carries them to and from the drive every cycle.

Step 1 — Create the FB Interface

In the project tree open Program blocks → Add new block, choose Function block, name it FB_VFD, set the language to LAD and click OK. Then fill in the block interface as below. The seven bits marked TRUE must be held at 1 for the drive to run, so they get TRUE as their default value — the OB1 call can then leave them unconnected.

With these defaults and ON_OFF1 at FALSE, the FB writes 16#047E to CW_01 from the first scan — the ready state. Setting ON_OFF1 changes it to 16#047F and the drive starts.

Step 2 — Write the FB Networks

The FB body is 34 Ladder networks: 16 for the control word, 16 for the status word and 2 for speed scaling. The operand names match the interface above.

Control word — Networks 1 to 16

Status word — Networks 17 to 32

Speed scaling — Networks 33 and 34

16#4000 (16384) equals 100 % of p2000. Replace 1500.0 with your drive's p2000 reference speed in rpm.

Step 3 — Call the FB in OB1

Open Main [OB1] and drag FB_VFD from the project tree into network 1. TIA Portal asks for an instance data block: name it DB_VFD_01 and click OK. Then connect the pins as shown. Pins showing ... are left unconnected and use their default value from the interface.

Motor1_Ack_Pulse must be a short pulse of around 200 ms — for example from a TP timer triggered by the reset button — never a held signal, because fault acknowledge works on the rising edge.

Step 4 — Map to I and Q Addresses

The addresses come from the hardware configuration, not from the program. In Devices & networks, double-click the G120, open the Device view and look at the Device overview table. The row Standard telegram 1, PZD-2/2 shows an I address range and a Q address range — for example 256…259 for both.

Create the tags in a PLC tag table with these names, types and addresses. The list below includes the machine tags used in the OB1 call.

// PLC tag table - drive 1 (addresses from the G120 Device overview)
G120_1_CW_01        Word  %QW256   // PZD1 out - STW1 control word
G120_1_CW_02        Word  %QW258   // PZD2 out - NSOLL_A speed setpoint
G120_1_SW_01        Word  %IW256   // PZD1 in  - ZSW1 status word
G120_1_SW_02        Word  %IW258   // PZD2 in  - NIST_A actual speed
// Machine tags used in the OB1 call
Motor1_Run          Bool  %M10.0   // Run command to ON_OFF1
Motor1_Ack_Pulse    Bool  %M10.1   // 200 ms reset pulse to Ack_Flt
Motor1_Running      Bool  %M10.2   // From Oper_En - HMI lamp and interlocks
Motor1_Fault        Bool  %M10.3   // From Fault
Motor1_Warning      Bool  %M10.4   // From Warning
HMI_Set_RPM         Real  %MD20    // Speed setpoint in rpm to Set_RPM
HMI_Act_RPM         Real  %MD24    // Actual speed in rpm from Act_RPM

If the hardware address ever changes, edit only the four G120_1_ tags. The FB and the OB1 call stay untouched.

Adding a Second Drive

Add a second network in OB1, drag in FB_VFD again and create a new instance DB, DB_VFD_02. Connect it to the second drive's telegram addresses and its own machine tags. The FB code is not copied or changed.

The second drive's addresses above are examples. TIA Portal assigns them when the drive is added, so always read them from that drive's own Device overview.

This block is the PROFINET route. For the other options in Siemens PLC and VFD networking, including USS, Modbus and hardwired control, see the overview.