FM 354 Jogging Mode Setpoint: Configuring Speed vs Position

The Siemens FM 354 servo positioning module is a frequently deployed positioning controller on S7-300 stations. Engineers commissioning it commonly encounter a situation in which the configured setpoint reads zero in the online view, particularly in jogging mode. The root cause is rarely a wiring or initialization fault: the FM 354 treats jogging as a speed-controlled operating mode and does not accept a position setpoint at all. This article resolves the setpoint zero issue, maps the relevant DBD/DBX addresses in the user DB, and walks through the correct commissioning sequence for jogging, incremental, and MDI/Automatic modes. For background, see the Siemens Industry Online Support entry for FM 354 (6ES7354-1AH01-0AE0).

1. FM 354 Operating Mode Matrix

The FM 354 supports five principal operating modes, each with a different setpoint semantic. Selecting the right setpoint register requires understanding the mode being executed. The full mode set is documented in the FM 354 function manual.

The most common commissioning error is loading DBD 322 (an absolute position target) into the module while it is in jogging mode. The FM 354 ignores DBD 322 in jogging mode because there is no target position to reach. The "zero" you read is the correct value: the module reports that no absolute setpoint is active.

2. Why the Online View Shows Zero

In the FM 354 online/start-up window, the displayed fields are read directly from the user DB and the module's internal status. The setpoint display reflects what the operating mode currently consumes:

• Jogging mode: the "setpoint" field mirrors the position command being internally generated. While no jog direction is active, the integrated position command is zero, and the display updates only while JOG+ or JOG- is asserted.
• Incremental mode: the value in DBD 156 is consumed as the relative increment length. The on-screen target position stays at zero until the start edge is applied.
• MDI / Automatic mode: DBD 322 is the absolute target. Display zero means the register has not been written by the PLC application, or the move has already completed and the register is stale.

If you have completed the preconditions listed in Section 4 and the setpoint field still reads zero, the next sections tell you which register to write for the mode you are actually using.

3. User DB Layout: Control, Mode, and Setpoint Areas

The FM 354 reads its I/O from a user DB that the configuration tool creates and assigns to the module. The DB layout is fixed by the FM 354 firmware and is documented in the Siemens FM 354 function manual. The relevant fields for the jogging / setpoint question are:

When you write a value to DBD 322 in jogging mode, the FM 354 simply does not consume that register. That is the expected behavior. Conversely, DBD 156 in jogging mode is also ignored because the module never executes an incremental move while in jogging mode.

4. Required Preconditions and the Initialization Sequence

Before any setpoint is acted on, the FM 354 expects a fixed start-up sequence. Skipping any of these leaves the module in a state where it accepts writes but executes no motion, and the online view reads zero for all motion fields.

1. Hardware configuration — FM 354 inserted in the S7-300 rack with the correct order number (for example 6ES7354-1AH01-0AE0) and assigned a user DB by the configuration tool.
2. Machine data download — MD file transferred to the module; module reports "initialized" on the diagnostic LEDs.
3. Drive Enable (AF, DBX 15.7 = 1) — the digital drive stage is released. AF=0 locks all motion.
4. Stop (STP, DBX 15.1 = 0) — explicit no-stop condition. STP is active when 1, so the application must drive it low.
5. Servo Enable (RF, DBX 34.0 = 1) — the position controller is closed. Without RF, the regulator output is zero and the axis will not move even if a setpoint is present.
6. Mode selection and acknowledgment — write the mode code, then toggle the mode-acknowledge bit per the FM 354 handshake.
7. Speed levels transferred — for jogging, the configured jog/creep/approach speed set must be downloaded as part of the MD set; the module references those speeds internally.

5. Jogging Mode: The Correct Setpoint Path

Jogging on the FM 354 is fundamentally a speed-control mode. The application does not write a target position. Instead, the operator presses a JOG+ or JOG- pushbutton (wired to digital inputs or written into the user DB), and the FM 354 internally generates a position command that ramps the axis to the configured jog speed. The basic speed-control relationship the FM 354 applies internally is:

v(t) = v_jog · ramp(t)        // configured jog speed, ramped
x(t) = ∫ v(t) dt                 // position command = integral of commanded speed

The relevant user-DB control bits in jogging mode are:

Speed selection comes from the configured speed table — typically JOG_SPEED_V1 / JOG_SPEED_V2 as set in the machine data — and is selected either by a digital input or by a control bit depending on how the project was parameterized. There is no user-DB register in which you can write an arbitrary jogging speed at runtime on the FM 354; the speed is fixed at configuration time. If you need a variable jog speed, you must switch between configured speed levels (V1 / V2).

While the JOG bit is asserted, the FM 354 ramps the internal position command at the configured acceleration. The "setpoint" field you see online is the result of that integration; it changes only while the bit is asserted. Releasing the bit causes the FM 354 to ramp the position command back to a stop. The display reading zero in idle is therefore correct, not a fault.

6. Incremental Mode: Why DBD 156 Is the Right Register

In incremental mode, the FM 354 executes a fixed-length move. The relative distance is set in DBD 156 (named INC_LENGTH in the FM 354 documentation) and is interpreted in the configured position unit (increments, mm, or degrees). On the start edge, the FM 354 takes the value in DBD 156, ramps the axis to the configured increment speed, and decelerates so the axis stops exactly INC_LENGTH from the start point.

If you wrote DBD 322 instead, the FM 354 interpreted it as an MDI absolute target, which is not what incremental mode expects. In some FM 354 firmware versions, a stale value in DBD 322 in incremental mode is ignored entirely, and the move either does not start or stops at the next sync point with zero displacement. That is the second source of the "setpoint reads zero" symptom.

Procedure for incremental mode:

1. Set AF=1, STP=0, RF=1 as in Section 4.
2. Switch to incremental mode and acknowledge.
3. Write the desired increment in user units to DBD 156 — for example L +5000.0; T DBD 156 for a 5000-unit positive move.
4. Pulse the start edge (DBX start or the dedicated increment start bit per the user DB layout).
5. Monitor the actual position and the running setpoint in the online view; the displayed setpoint will ramp as the move progresses.

7. MDI and Automatic Mode: DBD 322 (SET_POS) Usage

DBD 322 is the MDI absolute target position. It is consumed only when the FM 354 is in MDI mode and the MDI block has been started. Typical usage:

1. Set AF=1, STP=0, RF=1.
2. Switch to MDI mode and acknowledge.
3. Write the target coordinate to DBD 322 — e.g. L 1.234E+02; T DBD 322 for a 123.4-unit absolute target.
4. Optionally write the MDI speed and acceleration override to the corresponding user-DB words.
5. Pulse the MDI start edge. The FM 354 will move the axis to the absolute coordinate stored in DBD 322.

Automatic mode uses a block program stored in the FM 354; DBD 322 is not the right way to inject positions in automatic mode. The PLC should issue block numbers, G-functions, and target coordinates via the appropriate automatic-mode registers described in the FM 354 manual.

8. STEP 7 Logic Snippets for Each Mode

The following STEP 7 STL snippets show the minimum control logic for each mode. Adapt to your project, but the bit/register mapping is canonical for the FM 354 with the default user DB.

Jogging mode — one-shot commissioning block

// Always-on interlock
AN "STP_PB"            // pushbutton or program stop
= DBX 15.1             // STP = 0 (no stop)

A "AF_REQ"             // drive enable request from HMI
= DBX 15.7             // AF = 1

A "RF_REQ"             // controller enable request
= DBX 34.0             // RF = 1

// Jog direction
A "JOG_PLUS"           // JOG+ pushbutton
= DBX 16.0             // JOG+ bit per user DB
A "JOG_MINUS"          // JOG- pushbutton
= DBX 16.1             // JOG- bit per user DB

Incremental mode — single 5000-unit move

// Mode select = Incremental (per FM 354 mode code table)
L 2
T DBB 15
SET
S DBX 14.0            // Mode acknowledge edge per user DB

// Increment length
L +5.000E+03
T DBD 156             // INC_LENGTH

// Start edge
A "INC_START"
S DBX 14.1            // Increment start bit

MDI mode — move to absolute target

// Mode select = MDI
L 3
T DBB 15
SET
S DBX 14.0            // Mode acknowledge

// Absolute target
L 1.234E+02
T DBD 322             // SET_POS

// MDI speed override (example: 50% of configured)
L 50
T DBW 326             // MDI_SPEED override register

// Start
A "MDI_START"
S DBX 14.2            // MDI start bit

9. Online Diagnosis: What the Start-Up Window Actually Shows

The FM 354 online / start-up window in the configuration tool provides a real-time view of the user DB and the module status. The columns to watch:

A zero setpoint is only a fault when the application has commanded motion (e.g. JOG+ is asserted, or a move start edge has been issued) and the setpoint is not ramping. In that case, the cause is upstream: AF, STP, RF, or mode acknowledgment. The setpoint registers DBD 156 / DBD 322 are not involved.

10. Verification Procedure

After reconfiguring, run this verification sequence to confirm the FM 354 responds to jogging commands.

1. In the FM 354 configuration tool, go online and open the start-up window.
2. Confirm AF=1, STP=0, RF=1 in the live DB view.
3. Confirm the mode indicator shows "Jogging" and that mode acknowledge has completed (no mode-change error bit set).
4. Press and hold JOG+ via the HMI or by writing the corresponding DBX bit. The setpoint position and setpoint speed fields must ramp from zero toward the configured jog speed, and the actual position must follow.
5. Release JOG+. The setpoint speed must ramp to zero; the axis must stop within the configured deceleration time.
6. Repeat with JOG- and confirm negative direction.
7. Switch to incremental mode, write INC_LENGTH=5000 to DBD 156, and trigger the start edge. Confirm the displayed target advances by 5000 units and that the axis stops at the new position with following error returning to zero.
8. Switch to MDI mode, write SET_POS=123.4 to DBD 322, and trigger the MDI start. Confirm the axis moves to the absolute coordinate.

11. Troubleshooting Matrix

12. Common Pitfalls, Field Notes, and Migration

Three patterns recur on commissioning calls:

1. Mixing user-DB conventions between FM 354 and FM 357-2 / FM 458. The FM 357-2 and FM 458 use a different user-DB layout. Do not copy a working FM 357-2 user DB into an FM 354 project. Re-create the user DB from the FM 354 configuration tool.
2. Re-writing DBD 322 every OB1 scan. If the application writes SET_POS from a process variable that updates faster than the FM 354 consumes it, the displayed target can appear to "flicker" or be overwritten mid-motion. Latch the setpoint at the start edge and do not update until the FM 354 acknowledges the move (in-position flag set).
3. Confusing the displayed setpoint with the user-DB register. The online window label "setpoint" refers to the internal command value, not to DBD 322 or DBD 156. Writing to those registers does not change the displayed setpoint in jogging mode, because jogging mode does not consume them. Verify by writing to the correct register and then issuing a start edge; the setpoint column should ramp.

The FM 354 is end-of-life and replaced in the S7-300 family by positioning functionality integrated into the CPU (S7-300 CPU 315T/317T) and by the FM 357-2 / IM 174 / S7-1500 TM PTO modules. The setpoint concept is similar but the user-DB layout differs. The same diagnostic principle applies: jogging on any Siemens positioning platform is a speed-controlled mode, and the user-DB "position setpoint" register is only consumed in MDI/Automatic modes. For projects migrating from FM 354 to S7-1500 Motion Control, see the S7-1500 Motion Control function manual: map jogging to MC_MoveJog (Velocity mode), incremental moves to MC_MoveRelative, and MDI moves to MC_MoveAbsolute. The mental model of "jogging has no position setpoint; incremental/MDI do" carries over.