SINAMICS V20 Digital Outputs: Source Selection and Fault Response

SINAMICS V20 Digital Output Hardware Overview

The SINAMICS V20 is a compact, basic-class frequency inverter from Siemens available in 230 V 1AC and 400 V 3AC supply variants from 0.12 kW to 30 kW. Although Siemens markets the V20 as a “basic inverter,” the digital I/O structure is fully parameter-driven and supports status-word bit routing, BICO interconnects, and application-defined fault reactions through the standard parameter set.

Two physical digital outputs are provided on the control board:

• DO1 — Transistor output (open-collector / source-style 24 V output stage referenced to terminal 14 common)
• DO2 — Relay output (changeover / SPDT contact, terminals 18-19-20)

The hardware distinction matters: DO1 is suitable for low-power signal-level tasks (driving a PLC input, LED indicator, or low-current 24 V load), while DO2 with its dry contact is intended for switching auxiliary circuits such as contactors, brake releases, or annunciator relays. The selection of the logical source driving each output is independent of the hardware type and is governed by parameters P0731 (DO1) and P0732 (DO2).

DO1 and DO2 Terminal Identification and Electrical Ratings

Output Source Selection Parameters P0731 and P0732

The parameter list in the SINAMICS V20 Operating Instructions defines P0731 as “Selection of digital output 1 source” and P0732 as “Selection of digital output 2 source.” The accepted values are BICO-style indices pointing to a bit of a status word, comparator output, or logic-gate output.

Factory defaults shipped from Siemens:

• P0731 = 52.3 — DO1 reflects bit 3 of status word 1 (r0052.3 = “Inverter fault active”)
• P0732 = 52.7 — DO2 reflects bit 7 of status word 1 (r0052.7 = “Inverter warning active”)

To re-route a digital output, the parameter is written using the BICO form ww.xx, where ww is the parameter number of the source word (for example 52, 53, 3113) and xx is the bit index (0–15) within that word. The V20 BOP (Basic Operator Panel) and the SINAMICS V20 Smart Access Web Server both accept this compound value.

Status Word 1 (r0052) Bit Mapping

Status word 1, parameter r0052, is the primary assignment pool for digital output source selection. The first 16 bits (r0052.0 through r0052.15) each represent a discrete operating condition. The most commonly used bits for external signalling are listed below.

Status Word 2 (r0053) Bit Mapping

Status word 2 (r0053) carries the drive-internal control flags and is equally valid as a digital output source.

When using frequency or speed comparisons, verify the relevant threshold parameters (P1080, P1082, P2155, P2161, P2167) are populated to expected values, otherwise the bit remains at a fixed logic level.

BICO and Logic-Gate Source Options

Apart from raw status-word bits, the V20 supports a small library of internal logic resources. Each can be addressed by its parameter number and bit index and assigned to P0731 / P0732 just like a status word.

• r2811 — Output of AND gate 1
• r2812 — Output of AND gate 2
• r2813 — Output of AND gate 3
• r2814 — Output of OR gate 1
• r2815 — Output of OR gate 2
• r2816 — Output of OR gate 3
• r2817 — Output of XOR gate 1
• r2818 — Output of XOR gate 2
• r2819 — Output of NOT gate 1
• r2820 — Output of NOT gate 2

These gates are the building blocks for composite conditions such as “run AND above frequency threshold” or “fault OR warning.” The gate inputs are configured with P2810[0..1] for AND1, P2820-style input mappings, and so on. Use r2811 as a runtime probe to verify AND-gate logic while commissioning.

Configuring DO1 to Trigger on Modbus Communication Loss

A common use case is to release a digital output when the upstream Modbus master drops the bus, allowing the drive to fall back to a hard-wired safety state. The V20 exposes a watchdog fault (F72 / fault code 72) generated after a Modbus telegram timeout configured through P2040 and P2041.

1. Set P2040 = time in ms for telegram timeout (for example 1000 ms).
2. Set P2041 = 0 (Modbus) or 2 (USS on RS485) as the relevant fieldbus profile.
3. Confirm the default mapping: fault 72 is raised and routes through the standard fault reaction path.
4. Assign P0731 to 52.3 (the default) so that DO1 goes low (energized-relaxed) the moment the fault becomes active.
5. If the default reaction is too aggressive, override the reaction with P2101[x] = 0 (no reaction) and use only the DO as an indicator, leaving the drive to continue from last setpoint.

Verify by physically disconnecting the RS485 cable; DO1 should change state within the P2040 timeout window. The transistor on DO1 inverts with fault logic: drive OK = HIGH, fault active = LOW (or vice versa depending on internal pull-up configuration of the control board variant).

Motor Cable Fault Detection on the V20

The V20 does not provide a dedicated “output phase loss” bit in the same way that higher-tier SINAMICS platforms do. The following bits are the closest available signals and can be routed to DO1 or DO2:

Fault Number and Reaction Configuration (P2100 / P2101)

The V20 supports user-defined fault numbers in the range of P2100, with the response behaviour defined in P2101 at the same index. To override the default reaction of any fault code:

1. Set P2100[0] to the fault number whose reaction is to be changed (for example 72 for Modbus timeout, 1 for inverter overtemperature, 2 for overcurrent).
2. Set P2101[0] to one of the reaction codes: 0 = no reaction, 1 = OFF1 (ramp stop), 2 = OFF2 (coast), 3 = OFF3 (quick-stop ramp).

Multiple fault/reaction pairs may be entered by extending the indices: P2100[0] / P2101[0] through P2100[4] / P2101[4] depending on firmware revision.

Ramp Stop Methods: OFF1, OFF2, OFF3

For machinery where an immediate DO-triggered stop on Modbus loss could damage the product (the source author’s specific concern), set the corresponding P2101 reaction to OFF1 or OFF3 so the ramp times govern the stop, not an abrupt OFF2. Use the digital output only as a status annunciator in that scenario.

Complete Parameter Reference

Commissioning and Verification Procedure

1. Read the active state of the digital output by monitoring r0052 in its entirety on the BOP (navigate to r0052 and use the bit-toggle key to view bits 0–15).
2. Identify the bit representing the desired event (for example r0052.0 = drive ready, r0052.3 = fault active).
3. Write the BICO value ww.xx (for example 52.0) to P0731 or P0732, where ww is the status word parameter and xx is the bit index.
4. Force the event locally: trigger a fault by writing P2100[0] = 1 and P2101[0] = 2, or remove a digital input wiring to simulate run inhibit.
5. Measure the output terminal voltage with a multimeter: DO1 should swing between 0 V and 24 V DC; DO2 contact should open or close per the source bit.
6. Reset all test entries before returning the drive to production service: zero out P2100 / P2101 test entries, restore P0731 / P0732 to their final assigned values, and perform a save (set P0010 = 30, then P0971 = 1 to write to non-volatile).

Troubleshooting Matrix