SINA_POS FB284 Brake Control and Homing on SINAMICS S110

1. Overview of SINA_POS (FB284) and SINAMICS S110 Positioning

The SINA_POS function block (FB284) is the Siemens-standard application block for positioning a single SINAMICS drive from a SIMATIC S7-1200 or S7-1500 controller. The block is delivered as part of the SINAMICS Blocks for S7-1200/S7-1500 library and is inserted into the TIA Portal project with its own instance data block (DB). FB284 cyclically exchanges process data (PZD) with the drive over PROFINET using a configured standard telegram 111, which is the predefined telegram for "positioning drive with extended functions".

The hardware topology assumed in this article is:

• Controller: SIMATIC S7-1214C PN (DC/DC/DC or DC/DC/Rly variant, firmware V4.2 or higher recommended).
• Drive: SINAMICS S110 (CU305 PN) with a connected 1FK7/1FT7/1FL6 servo motor.
• Brake: Motor holding brake (integrated 24 V brake) or external holding brake, switched by a SIRIUS contactor driven from a digital output of the S7-1200.
• Homing sensor: Mechanical limit switch or proximity sensor wired to a digital input of the S7-1200.
• PROFINET IO: Telegram 111 mapped into FB284 instance DB slots.

The standard FB284 user interface exposes a structured set of inputs and outputs (iAxisMode, eiMode, lrPosition, lrVelocity, bStart... commands) but it does not expose a dedicated manual brake input or a homing switch input. Both functions have to be implemented on top of FB284 by reading from and writing to the instance DB's cyclic send/receive buffers (sxSendBuf, sxRecvBuf) and by driving the brake through a free PLC output. The remainder of this article documents exactly that procedure using only official Siemens documentation as reference.

2. Prerequisites and Telegram 111 Configuration

Before opening the instance DB, the project must satisfy the following prerequisites:

1. TIA Portal V15.1 or higher (FB284 V4.x supports the current S110 firmware; older portal versions ship older FB revisions that are not bit-compatible).
2. SINAMICS Blocks for S7-1200/S7-1500 library installed and up to date. The library is delivered through the Siemens Support entry 109750451 and is also available in the TIA Portal "Libraries" task card.
3. SINAMICS S110 firmware V4.7 or higher (older V4.4 still works for the basic positioning set, but the homing state-machine bits in ZSW1 follow V4.7 mapping).
4. PROFINET device configuration: the S110 must be inserted in the device view of the S7-1214C PN and the slot "Telegram 111" must be assigned to the appropriate submodule.
5. Drive parameterization in Startdrive or STARTER (commissioning tool of the S110):
   • p922 = 111 (PROFIdrive telegram selection = standard telegram 111)
   • p1001 = 2 (Position control activation, EPOS mode)
   • p2502 = 1 (Linear axis scaling)
   • p2503 = 1 (LU/1000 µm or 1 LU = 1 motor revolution depending on mechanical configuration)
   • p2580 ... p2592 for the EPOS operating modes
   • p1215 = 0 (motor holding brake not controlled by drive-internal sequence, because the brake is being controlled externally by the PLC)
6. PROFIsafe / Safety Integrated is outside the scope of FB284. The holding brake release must be wired through a safety relay if the application is in category 3 PL d or higher. The Siemens S110 Safety Integrated manual describes the SS1/STO path.

The full library and block overview is published in the Function blocks to control the SINAMICS with SIMATIC S7 in TIA application note. The SINA_POS chapter begins on page 47 and lists every input/output variable in the block interface.

3. SINA_POS Instance DB Structure and Bit Access

When the SINA_POS FB is instantiated, TIA Portal creates a typed instance data block (for example, SINA_POS_DB). The structure of that DB is the key to controlling the brake and the homing sequence from the S7-1200. The two most important substructures are:

• sxSendBuf – the cyclic output process image sent from PLC to drive (PZD1..PZD16).
• sxRecvBuf – the cyclic input process image received from drive (PZD1..PZD16).

With standard telegram 111, the first two PZD words are mapped as follows:

Each individual bit of a WORD can be accessed from SCL or LAD/FBD with the standard S7-1200 syntax "SINA_POS_DB".sxSendBuf.STW1.%X2. The struct access is allowed because the FB284 instance DB is a fully typed DB; the compiler enforces that the bit belongs to the correct send/receive buffer.

4. Homing Sequence with External PLC Input

SINAMICS EPOS supports several referencing modes. With telegram 111 and SINA_POS FB284, the homing sequence is initiated by setting three bits in PosStw (the positioning control word) in the correct order. The PLC input that is wired to the homing proximity switch is then evaluated by the drive, not by the PLC, once the homing run is started. This is the cleanest architecture because the drive already knows the encoder reference position.

Homing requires three sequential control bits (see G120 SINA_POS documentation, chapter 4.4):

1. Set referencing bit – PosStw.%X0 = TRUE (mode "Reference approach").
2. Start referencing – rising edge on PosStw.%X1 (rising edge is mandatory, the bit is processed in EPOS state machine).
3. Wait for feedback – monitor ZswRecv.PosZsw.%X1 (reference point set) and ZswRecv.PosZsw.%X2 (reference point approach complete).

The S7-1200 side of the program is therefore only responsible for:

• Reading the homing switch digital input (e.g. %I0.3).
• Debouncing the input with TON/TOF if the sensor is mechanical.
• Generating the rising edge on the EPOS start bit.
• Clearing the start bit after the homing run has completed (otherwise EPOS will re-trigger the homing run on the next cycle).

Sample SCL code that wraps the bit access into a clean function block:

// Homing sequence wrapper for SINA_POS FB284
FUNCTION_BLOCK "fbHomingS110"
VAR
    iHomingSwitch AT %I0.3 : BOOL;   // prox switch wired to S7-1200
    bStartHoming   : BOOL;            // HMI start command
    tDebounce      : TON;             // 50 ms debounce
END_VAR
BEGIN
    // 1. debounce the mechanical homing switch
    tDebounce(IN := iHomingSwitch, PT := T#50ms);

    // 2. request "reference approach" mode (PosStw bit 0)
    "SINA_POS_DB".sxSendBuf.PosStw.%X0 := NOT "SINA_POS_DB".sxRecvBuf.PosZsw.%X1;

    // 3. generate the rising edge to start the homing run (PosStw bit 1)
    IF bStartHoming AND tDebounce.Q THEN
        "SINA_POS_DB".sxSendBuf.PosStw.%X1 := TRUE;
    ELSIF "SINA_POS_DB".sxRecvBuf.PosZsw.%X1 THEN  // home position reached
        "SINA_POS_DB".sxSendBuf.PosStw.%X1 := FALSE;
    END_IF;

    // 4. publish the status to the HMI
    bHomingActive    := "SINA_POS_DB".sxRecvBuf.PosZsw.%X0;
    bHomePositionOK  := "SINA_POS_DB".sxRecvBuf.PosZsw.%X1;
END_FUNCTION_BLOCK

The S110 drive parameters that match this sequence are p2595 = 1 (active homing with zero mark), p2596 = 0 (use proximity switch on DI0 of the S110), or, if the homing sensor is wired only to the PLC, p2596 = 4 (external homing via telegram bit). The selection of p2596 is what allows the PLC to inject the homing event entirely through the PROFINET telegram.

5. Manual Brake Control Architecture

The SINAMICS S110 can manage a 24 V holding brake in two distinct ways:

1. Drive-internal brake control – the CU305 PN applies/removes 24 V on the X6.3 / X6.4 terminals in sync with the enable/disable sequence, configured through p1215 = 1.
2. External (PLC) brake control – the drive is parameterized with p1215 = 0; the S7-1200 drives a digital output that energises a contactor or solid-state relay wired to the brake.

When the brake must follow a discrete PLC input (for example a jog PB on the HMI, or a manual override signal that releases the brake only on operator command), the second approach is the right one. The drive has to be told that it is not managing the brake, and the PLC has to handle all the timing.

Recommended wiring:

• CPU digital output, e.g. %Q0.5, wired to a SIRIUS 3RT2015 contactor coil (24 V DC).
• Contactor main contacts in series with the motor brake leads (white / black on a 1FK7 motor).
• An additional hardwired enable: the contactor is only allowed to close when the drive is in state Operation enabled (ZSW1 bit 2 = 1) and the operator's manual PB is pressed.

Sample SCL code for the manual brake output, using the SINA_POS instance DB to read the drive state and a free PLC input to take the manual release command:

// Manual brake control wrapper
FUNCTION_BLOCK "fbManualBrakeS110"
VAR
    bManualReleasePB AT %I0.4 : BOOL;     // operator push-button
    bDriveStandstill           : BOOL;
    bOperationEnabled          : BOOL;
    bBrakeOutput   AT %Q0.5    : BOOL;     // contactor coil
END_VAR
BEGIN
    bDriveStandstill  := "SINA_POS_DB".sxRecvBuf.ZSW1.%X7;   // 1 = standstill
    bOperationEnabled := "SINA_POS_DB".sxRecvBuf.ZSW1.%X2;   // 1 = operation enabled

    // Brake only released if:
    //  - drive is standing still (avoid release while running)
    //  - drive is operation-enabled (avoid release when STO active)
    //  - operator is pressing the manual release push-button
    bBrakeOutput := bDriveStandstill
                    AND bOperationEnabled
                    AND bManualReleasePB;
END_FUNCTION_BLOCK

6. STW1 Control Word Bit Map (Telegram 111)

The PROFIdrive control word STW1 is the master enable word of the drive. FB284 fills STW1 with the logical combination of the S7-1200 inputs and its internal state machine. The bits below are the ones most relevant when integrating a manual brake and a homing run; the layout is identical to the SINA_POS reference documentation.

When p1215 = 0 the drive does not attempt to drive the brake; bit 11 of STW1 is then internally ignored. This is the only way to guarantee that the PLC has full authority over the brake.

7. ZSW1 Status Word Bit Map (Telegram 111)

ZSW1 is what the PLC uses to read the drive state. The two bits needed for safe manual brake operation are bit 2 (Operation enabled) and bit 7 (Standstill).

Both ZSW1 bits must be combined with the manual PB on the HMI before the PLC drives the brake output. The "Standstill" bit is the key interlock that prevents the brake from being released while the motor is still rotating.

8. Hardware Wiring for External Brake

The motor holding brake on a 1FK7/1FT7/1FL6 is a 24 V single-coil brake. The lead colours are typically white (+) and black (–). The recommended drive-side wiring is:

• Direct drive control (p1215 = 1): connect the brake leads to X6.3 (+) and X6.4 (–) of the CU305 PN. The drive's internal sequence takes care of the timing.
• PLC control (p1215 = 0): do not connect the brake leads to the CU305 PN. Bring them out of the motor cable through a separate terminal block and route them through a SIRIUS 3RT contactor or a 3RF solid-state relay driven by the S7-1200 output.

It is strongly recommended to put a free-wheeling diode (1N4007) across the brake coil when using a DC contactor, and a varistor (SIOV-S07K25) when using a 24 V solid-state relay. The brake is highly inductive and the suppression device must be on the coil side, not on the contact side.

9. Step-by-Step TIA Portal Configuration

1. Insert the S110 from the hardware catalog (TIA Portal V15.1 or later) and assign the PROFINET device name S110_1.
2. In the device view, change the inserted submodule to Telegram 111 (the default is Telegram 1 for basic speed control). The slot is "DO with PROFIdrive / Telegram 111 / Position control".
3. From the SINAMICS library, drag SINA_POS (FB284) into the program and call it with a multi-instance DB or a single instance DB (e.g. SINA_POS_DB). Wire the HWID of the Telegram 111 submodule to iDriveID, and the encoder data (single turn, multi turn) to the appropriate inputs.
4. Open the drive in Startdrive and go online. Set the following parameters:
   • p922 = 111
   • p1001 = 2 (EPOS activated)
   • p1215 = 0 (no internal brake)
   • p2595 and p2596 to match the homing switch wiring (either drive-side DI or telegram bit)
5. Compile and download the S7-1200 project. Go online in TIA Portal and open SINA_POS_DB in watch mode. Verify that the cyclic send buffer sxSendBuf.STW1 and the cyclic receive buffer sxRecvBuf.ZSW1 are both being updated. The initial value of STW1 must be 16#047E (drive commanded to ON, OFF2/OFF3 inactive, control by PLC).
6. Insert the fbHomingS110 and fbManualBrakeS110 blocks from sections 4 and 5. Wire the homing switch input and the manual brake output to the actual I/O.
7. Force the manual release PB and confirm that the contactor energises, the brake releases, and the motor can be turned by hand. Release the PB and confirm that the brake falls.
8. Trigger the homing run from the HMI and confirm the PosZsw bits toggle as documented in section 4.

10. Verification and Commissioning Procedure

After the configuration is complete, run the following checks in order. Each step is mandatory before the machine can be released for production.

11. Fault Handling and Diagnostics

The S110 reports faults and warnings both in the cyclic ActFault / ActWarn words of FB284 and in the drive's own fault buffer. The most common fault numbers for the brake and homing path are listed below.

The fault numbers are documented in the S110 List Manual. Acknowledge the fault from the PLC with a rising edge on STW1.%X7 after the drive has reported "Switch-on inhibited" (ZSW1.%X6 = 1).

12. Frequently Asked Questions