Configuring 7 PTO Outputs on S7-314 2DP: FM and ET 200S Solutions

Generating seven independent pulse train outputs (PTO) from a SIMATIC S7-314 2DP CPU is a recurring engineering question because the standard S7-314 2DP (6ES7314-6CG03-0AB0 or equivalent order numbers) does not include on-board PTO channels. Only the compact CPUs of the S7-300 family (S7-312C, S7-313C, S7-313C-2 PtP, S7-313C-2DP, S7-314C-2 PtP, and S7-314C-2DP) ship with up to four integrated high-speed outputs. The "plain" 314-2DP without the "C" suffix has no pulse generator hardware at all, so any PTO requirement must be satisfied through function modules (FM), distributed I/O (ET 200S), intelligent drives, or a controller change.

This reference documents the four practical paths for delivering seven pulse-and-direction or CW/CCW pulse pairs to stepper or servo drives from an S7-300 station:

1. Four ET 200S 2-channel pulse modules 6ES7138-4DD01-0AB0 on a Profibus DP slave, producing eight 24 V pulse outputs up to 10 kHz each.
2. One or more FM 352-5 high-speed Boolean processors for high-speed pulse generation with ramp and direction control.
3. Migration of the motion task to an S7-1500 with TM PTO technology modules (4 channels per module, 24 V, up to 1 MHz).
4. Replacing PLC-side pulse generation with intelligent servo or stepper drives that accept setpoints over Profibus, Profinet, or analog/digital commands.

The remainder of this document covers hardware selection, electrical topology, STEP 7 / TIA Portal configuration, signal integrity constraints, and field-proven commissioning checks specific to driving seven axes from an S7-314 2DP.

Why the S7-314 2DP Cannot Generate PTO Directly

The S7-314 2DP CPU (order number 6ES7314-6EH04-0AB0 for the -2DP variant, depending on firmware release) provides:

• One Profibus DP master interface (X2).
• One MPI/Profibus combined interface (X1).
• No on-board digital outputs rated for high-speed pulse generation.
• No integrated technology functions such as positioning, counting in technology object form, or PTO.

By contrast, the S7-314C-2DP (6ES7314-6CG03-0AB0) integrates four 24 V high-speed outputs capable of PTO, PWM, and frequency output modes at up to 2.5 kHz from the standard technology objects. The user's station as described uses the non-"C" 314-2DP, so a different mechanism is required for each of the seven pulse streams.

Three electrical constraints govern every solution discussed below:

1. Output voltage. All Siemens S7-300 pulse outputs switch 24 V push-pull or PNP sourcing logic. This matches the standard differential line receiver inputs on modern stepper and servo drives (typically 5 V to 24 V opto-isolated inputs).
2. Output current. 24 V outputs from ET 200S pulse modules source typically 0.5 A per channel, with short-circuit protection. The cable length to the drive determines the capacitive load that limits maximum frequency.
3. Common-mode range. Differential receivers (RS-422 or 26LS31/26LS32 type) tolerate a common-mode range of typically -7 V to +12 V on the signal pair, which is comfortable for industrial cabinets. Refer to Texas Instruments differential PTO interface application brief (TIDUC30) for the receiver-side constraints.

Solution 1: ET 200S 2-Pulse Modules on Profibus DP (Recommended for ≤ 10 kHz)

The ET 200S distributed I/O family is the canonical answer for "I need more pulse outputs than the CPU has." The specific module is:

For seven PTO outputs, use four 6ES7138-4DD01-0AB0 modules on a single ET 200S Profibus DP slave. Eight channels are available; the eighth channel can serve as a spare, an electronic cam, or be disabled. The station is wired as follows:

• Interface module: IM 151-1 STANDARD (6ES7151-1AA05-0AB0) for Profibus DP, or IM 151-3 PN (6ES7151-3BA23-0AB0) if Profinet is preferred (the pulse module ships Profibus variant; the Profinet variant uses the same pulse module article number with the standard ET 200S Profinet backplane).
• Power module: PM-E 24 V DC (6ES7138-4CA01-0AA0) to provide 24 V to the electronic modules.
• Pulse modules: 4× 6ES7138-4DD01-0AB0 for 8 PTO channels.
• Digital inputs (optional): DI modules for home/reference switches, end limits, and drive enables.

Each pulse module channel exposes the following data in the Profibus cyclic I/O image:

Configuration Limits and Frequency Derating

The 10 kHz ceiling is not a hard limit of the silicon; it is the guaranteed frequency given worst-case cable capacitance of 2 nF per metre and a 30 m cable. If you wire the drive within 5 m of the ET 200S terminal block and use twisted-pair shielded cable, field installations have shown reliable operation at 20 kHz. However, treat 10 kHz as the engineering limit, especially when driving stepper motors where pulse rate sets the rotational speed:

For a 1.8° stepper motor (200 full steps per revolution) and a 10 kHz maximum pulse rate:

speed_rpm = (pulse_frequency / steps_per_revolution) * 60 speed_rpm = (10000 / 200) * 60 = 3000 rpm

If microstepping is used (e.g. 1/10 microstepping on a 1.8° motor = 2000 steps/rev), the maximum speed drops accordingly:

speed_rpm = (10000 / 2000) * 60 = 300 rpm

For servo drives, the pulse count is typically a fraction of the encoder resolution (e.g. one pulse = 1/4096 of a motor revolution if electronic gearing is 4096). The frequency ceiling is therefore usually acceptable for point-to-point positioning, but inadequate for continuous high-speed spindle-type applications.

Solution 2: FM 352-5 High-Speed Boolean Processor

The FM 352-5 is a function module that mounts in the S7-300 backplane and provides high-speed digital processing independent of the CPU scan time. The module is documented under the Siemens support entry for FM 352-5. Its primary use is high-speed Boolean processing at cycle times as low as 1 µs, but it is also capable of producing pulse trains with direction control and ramp-up/ramp-down profiles suitable for stepper drives.

Key parameters:

A single FM 352-5 can therefore deliver four pulse-and-direction channels at frequencies far above the 10 kHz limit of the ET 200S approach. To reach seven axes you would either:

• Use two FM 352-5 modules in the S7-300 rack (8 axes total), or
• Combine one FM 352-5 (4 axes, high speed) with one ET 200S 4×6ES7138-4DD01-0AB0 (8 channels, low speed), giving 12 axes from which 7 are used.

The FM 352-5 is configured with the included FM 352-5 Configuration Tool, which is launched from STEP 7. The configuration yields a DB (instance data block) plus an FB that the user program calls. The FB exposes inputs for target position, target velocity, acceleration, deceleration, and a start bit.

Ramp Profile Calculation

The trapezoidal velocity profile generated by the FM 352-5 follows standard motion equations. For an axis that must traverse a distance S in time T with constant acceleration a and deceleration -a:

v_max = (S / T) + (a * T / 4)    (trapezoidal, where T > sqrt(2*S/a))

For a triangular profile (no constant velocity segment), the peak velocity is:

v_peak = sqrt(a * S)    (triangular, where T = 2*sqrt(S/a))

The FM 352-5 accepts acceleration and deceleration in pulses/s² directly. For a servo with 4096 pulses/rev at a peak velocity of 3000 rpm (50 rev/s):

v_peak_pps = 50 * 4096 = 204800 pulses/s a_pps2 = 204800 / 0.05 s = 4,096,000 pulses/s² (50 ms to reach v_peak)

Confirm the value remains within the FM 352-5's 1 MHz ceiling, which it does by a factor of approximately 5. Slower ramps (200 to 500 ms) are typical in packaging machinery and remain comfortably within limits.

Solution 3: Migration to S7-1500 with TM PTO Technology Modules

If a controller change is acceptable, the S7-1500 platform is the modern answer. The TM PTO technology module (order numbers in the 6ES7553-1xxx0-xxx0 range, depending on output type) provides 4 high-speed PTO channels per module with the following documented characteristics (see Pulse Train Output (PTO) for S7-1500 in the TIA Portal Help):

• 4 PTO channels per TM PTO module.
• 24 V push-pull outputs, opto-isolated.
• Maximum output frequency up to 1 MHz per channel (configured per channel).
• Pulse-and-Direction or CW/CCW modes.
• Integrated homing, jog, and absolute/relative positioning technology objects in TIA Portal.
• Two modules (8 PTO channels) require only two free slots in the S7-1500 backplane.

For seven axes, two TM PTO modules deliver 8 channels with one spare. The configuration is performed entirely in TIA Portal V20 (or later) under Technology Objects → PTO. Each axis is configured with a technology object of type "PTO", with parameter sets for drive interface (output addresses), encoder feedback (optional), mechanical ratios, and dynamic limits.

For an S7-1500 system, the engineering effort is dramatically lower than for an ET 200S Profibus DP pulse module solution: the technology objects are pre-defined, the motion FB (MC_Power, MC_MoveAbsolute, MC_MoveRelative, MC_Home, MC_Stop) are part of the standard PLC open library, and diagnostic events appear in the TIA Portal online view with detailed cause codes.

Solution 4: Distributed Smart Servo Drives

A common modern architecture removes pulse generation from the PLC entirely. Each axis is driven by an intelligent servo drive (Siemens SINAMICS V90 with Profinet, or third-party units such as Yaskawa Sigma-7, Mitsubishi MR-JE, etc.) that accepts a setpoint position, velocity, or torque over a bus. The PLC computes the target and writes it via Profinet IRT, Profibus DP-V2, or even a single analog ±10 V command.

This approach scales to any number of axes (8, 16, 32, more) and decouples the motion controller cycle from the PLC OB1 scan. The downside is the higher per-axis cost of intelligent drives versus stepper drives, and the requirement for commissioning software per drive family.

Topology and Wiring

The typical cabinet topology for Solution 1 (ET 200S pulse modules) is illustrated below. The CPU S7-314 2DP acts as Profibus DP master. A single ET 200S station with IM 151-1 interface module houses the four pulse modules. Each pulse module routes PULSE, DIR, and ENA through a shielded twisted-pair cable to a stepper or servo drive. The 24 V power module in the ET 200S backplane supplies the pulse module logic, while the load supply to the drive is taken from a separate 24 V power supply with adequate current rating.

[CPU S7-314 2DP, X2: Profibus DP master] | | Profibus DP, 1.5 Mbps, 6XV1830-0EH10 cable | [IM 151-1 STANDARD] -> [PM-E 24 V DC] -> [6ES7138-4DD01-0AB0] ch1 --> Drive Axis 1 [6ES7138-4DD01-0AB0] ch2 --> Drive Axis 2 [6ES7138-4DD01-0AB0] ch3 --> Drive Axis 3 [6ES7138-4DD01-0AB0] ch4 --> Drive Axis 4 [6ES7138-4DD01-0AB0] ch5 --> Drive Axis 5 [6ES7138-4DD01-0AB0] ch6 --> Drive Axis 6 [6ES7138-4DD01-0AB0] ch7 --> Drive Axis 7 (ch8 spare / disabled)

Cable and Shielding Rules

• Use 24 AWG to 22 AWG (0.25 to 0.5 mm²) twisted-pair shielded cable, one pair per signal (PULSE/DIR share a 4-wire cable with ENABLE and ground return).
• Maximum recommended length: 30 m at 10 kHz; 10 m above 10 kHz; 3 m above 100 kHz.
• Ground the shield at the cabinet entry panel only; do not ground both ends (avoid ground loops).
• Separate the pulse cables from power cables by at least 200 mm, or use a divided cable tray.
• Twist the 24 V supply and 0 V return for each pulse module pair to cancel common-mode noise.

STEP 7 / TIA Portal Configuration

The exact configuration steps differ between STEP 7 V5.x (classic) and TIA Portal. Both ultimately generate a Profibus DP slave entry for the ET 200S station and place the pulse modules in the slot table. The procedure is summarized below for STEP 7 V5.7 (still common in brownfield S7-300 installations).

STEP 7 V5.x Configuration Steps

1. Open SIMATIC Manager and load the S7-300 station that contains the 314-2DP.
2. Open HW Config and select the ET 200S from the catalog under “Profibus DP → ET 200S”.
3. Drag the IM 151-1 STANDARD interface module to the Profibus subnet, assigning a unique DP address (e.g. 4).
4. Insert the PM-E 24 V DC power module in slot 1 of the ET 200S rack.
5. Insert four 6ES7138-4DD01-0AB0 modules in slots 2 through 5. Each occupies 2 bytes of output and 4 bytes of input in the Profibus I/O image.
6. Double-click each pulse module to open its properties. Set:
   • Operating mode = "Pulse output, pulse and direction" or "Pulse output, CW/CCW".
   • Output format = "Pulses per second (Hz)" or "Pulses per time unit" depending on the FB used.
   • Maximum frequency = 10000 (Hz) for 10 kHz applications.
   • Acceleration/deceleration = ramp time in ms (typical: 100 to 500 ms).
   • Diagnostics = enable "Short circuit" and "Missing load voltage".
7. Save and compile the HW Config. The cyclic I/O addresses are assigned automatically (e.g. Outputs 0..7 and Inputs 0..15 for the first module).
8. Use the Siemens standard FB "SFB 49" (Pulse Width Modulation) or the user FB from the ET 200S pulse module HSP to start, stop, and monitor each axis. Alternatively, integrate the pulse generation into the user's own OB1 logic, writing frequency and direction setpoints to the module's output words.

Structured Text Example: Starting Axis 1 at 5000 Hz, Direction = Forward

// Axis 1 control word - PULSE Module 1, Channel 0
// Output address from HW Config: QW 0 (control), QW 2 (frequency), Q0.0 (DIR bit)

// 1. Set direction = 0 (forward)
"Axis_1_DIR" := FALSE;

// 2. Wait one OB1 scan to allow the drive to latch direction
//    (Direction must be stable 1 ms before the first pulse edge)

// 3. Write frequency in Hz to the module's frequency setpoint word
"Axis_1_Freq_Word" := 5000;

// 4. Start the pulse generator by setting the start bit
"Axis_1_Start" := TRUE;

// 5. Pulse train begins on the next module cycle (~1 ms for the ET 200S pulse module)

Ladder Logic Example: Jogging Axis 3

// Network 1: Direction select
A     "Jog_Axis3_Forward"          // I0.5 - operator pushbutton
AN    "Jog_Axis3_Reverse"          // I0.6
=     "Axis_3_DIR"                 // Q4.0

A     "Jog_Axis3_Reverse"
AN    "Jog_Axis3_Forward"
=     "Axis_3_DIR_Reverse_Indicator"  // M20.0 (for HMI feedback)

// Network 2: Run with jog frequency
A     "Jog_Axis3_Forward"
O     "Jog_Axis3_Reverse"
AN    "Axis_3_Fault"               // I0.7 - drive OK contact
=     "Axis_3_Start"               // Q4.1 - latched to pulse module start bit

Pulse Train Output Signal Characteristics

The electrical interface of the pulse module outputs is identical to a Siemens 24 V digital output, with one critical caveat: the pulse rise and fall times determine the maximum usable frequency. The ET 200S 6ES7138-4DD01-0AB0 specifies a typical rise/fall time of 5 µs at 24 V / 0.5 A, which gives a clean edge up to about 50 kHz. The 10 kHz software limit is conservative, accounting for cable capacitance and opto-isolator rise times in the receiving drive.

For the FM 352-5, the eight high-speed outputs use differential 24 V line driver topology (RS-422 compatible) with rise times of 1 µs or less, enabling the 1 MHz maximum.

For a deeper discussion of the receiver-side requirements (common-mode range, input voltage tolerance, and cable capacitance limits) consult the Texas Instruments differential PTO interface brief (TIDUC30), which documents the SN75174 / SN75175 line driver/receiver family used in many stepper and servo drives.

Comparison Matrix: Which Solution for Which Application?

Commissioning and Verification

A structured commissioning sequence avoids the classic "it ran on the bench but not on the machine" surprises. The sequence below applies to the ET 200S pulse module solution; the FM 352-5 follows a similar logic with different parameter names.

1. Visual check. Verify the IM 151-1, PM-E, and four pulse modules are clipped into the TM-P or TM-B terminal modules with the bus connector tabs in place. Each pulse module should display a green SF (system fault) and a green BF (bus fault) LED off under normal conditions.
2. Profibus address. Confirm the IM 151-1 rotary switches match the configured DP address (e.g. 4). A mismatch is the most common cause of "slave not found" errors during PG online.
3. PG online. In STEP 7, go online with the CPU and open the ET 200S slave in HW Config. The slave should show "Module OK" for every slot. If a slot shows "Module not OK" or "Incorrect module in slot", check the article numbers and the terminal module keying (the mechanical coding on the TM-P terminals prevents insertion of the wrong module type).
4. Watch table test. Open a VAT watch table and force the output bits for axis 1: set the DIR bit to 0, set the start bit, and write 1000 to the frequency word. The drive should rotate at 1000 / 200 = 5 rev/s = 300 rpm for a 1.8° stepper with no microstepping. Use a handheld tachometer to verify the mechanical speed. Reverse the DIR bit and re-test.
5. Frequency sweep. With the drive disconnected (mechanical shaft free), sweep the frequency word from 100 Hz to 9000 Hz in 1000 Hz increments, holding each value for 2 seconds. The pulse module should not report a diagnostic interrupt, and the SF LED should remain off.
6. Load test. Reconnect the mechanical load and repeat the frequency sweep under torque. Monitor the drive's following error (or stepper stall flag) and confirm the motion completes without alarming.
7. Emergency stop verification. Trigger the E-Stop and confirm that all seven pulse generators stop within one Profibus cycle (typically 5 ms at 1.5 Mbps), and that the drive's STO (Safe Torque Off) input de-energises the motor within the time specified by the drive manual (typically 5 to 25 ms).
8. Diagnostic interrupt handling. Confirm that OB82 (diagnostic interrupt) is loaded in the CPU. The pulse module raises a diagnostic interrupt on short circuit, missing load voltage, or frequency overload. The interrupt OB must call the diagnostic FB to clear the condition or the module will remain in fault state.

Troubleshooting Matrix

Frequently Asked Questions