S+S Sestep 290/190 Programming Cable: RJ45 to DB9F Build Guide

Overview

The S+S Sestep 290 and 190 series drives require a dedicated programming cable to connect the drive's service port to a PC for commissioning, parameter upload/download, and firmware diagnostics. The factory-issued cable is an 8-position RJ45 (8P8C) to 9-pin D-Sub female (DB9F) assembly, generally supplied in a captive or semi-captive length. Field replacements are not always available through the original supply chain, so engineers frequently have to construct or source a third-party equivalent. This document consolidates the connector, signal, and verification information required to build a functional cable for these drives, including the variants that include a small interface PCB at the DB9 end.

The S+S Sestep product line is documented in legacy German-language datasheets. Service information is sparse in English and most surviving reference material is in the form of hand-drawn pinout diagrams. Engineers should treat the information below as a working reference and verify against any drawing shipped with the drive or its programming software.

Connector Identification

The programming port on the S+S Sestep 190/290 series is a male 8P8C modular jack (commonly referred to as RJ45) located on the front face of the control board or behind a small access cover, depending on the housing revision. The matching PC-side connector is a 9-pin D-Sub female (DB9F, also called a SUB-D Buchse). The German original drawings frequently label this as a "9-polige SUB-D Buchse" — "Buchse" translates to socket/jack, not plug, so any drawing showing a male D-Sub at the PC end is mislabeled.

When inspecting the connectors, observe them in face view (looking into the contacts):

• 8P8C RJ45 (drive end): 8 gold contacts visible in a single row, locking tab on top. Pin numbering follows the standard RJ45 convention: pin 1 is left-most with the locking tab on top and contacts facing you.
• DB9F (PC end): 9 sockets in two rows (5 on top, 4 on bottom). Pin numbering follows the EIA/TIA 574 standard: pin 1 is top-left, pin 5 is top-right, pin 6 is bottom-left, pin 9 is bottom-right when viewed face-on.

Cable Requirements

The S+S Sestep programming interface is a point-to-point serial link. From the limited published pinout references and the typical architecture of drives of this generation, the interface is consistent with an RS-232-style point-to-point link using three or more signal lines (TxD, RxD, and a ground reference), with optional hardware handshaking (RTS/CTS).

Recommended cable characteristics:

A cable with a small interface PCB inside the DB9 housing has been reported in the field. This PCB is not a true RS-232 line driver — it typically contains a few passive components (resistor dividers, protection diodes, or filter capacitors) to adapt the drive's logic levels or provide ESD suppression. If the original drawing does not produce a working link, the absence of this interface PCB in a hand-built cable is the most common root cause.

RS-232 Signal Mapping Considerations

The S+S Sestep 190/290 service port does not publish a public pinout that matches the EIA/TIA 574 PC standard. Field reports describe a 1:1 connection map in which the drive's TxD drives the PC's RxD and vice versa, but with two important caveats:

1. Logic level adaptation: The drive may use 0/5 V TTL-level signalling rather than true RS-232 (±12 V) on the RJ45 pins. If the cable routes these signals directly to the PC's RS-232 port, the link will fail or appear intermittent because most PC RS-232 receivers expect at least ±3 V. A MAX232-class level translator, or a passive charge-pump cable, is required in this case.
2. Loopback / handshaking: Some firmware revisions expect a hardware handshake loopback on the drive side. If the drawing shows a strap between two RJ45 pins that is not replicated in a hand-built cable, parameterisation software will time out without a connection.

Before committing to a wiring plan, obtain the original German datasheet ("S+S Sestep 190/290 Inbetriebnahme" or "Service-Anleitung") and cross-check the voltage levels on each pin with a multimeter in AC and DC mode. This is the single most useful diagnostic step when the published pinout does not produce a working cable.

Construction Approach

Two construction approaches are practical in the field: a passive straight-through cable and an active adapter cable. The choice is determined by whether the drive side uses TTL or RS-232 levels.

Approach A — Passive straight-through cable

Use this approach if measurement confirms ±5 V to ±12 V signals on the RJ45 pins.

1. Cut an 8-conductor shielded cable to the required length (typically 2–3 m).
2. Crimp an RJ45 plug using the T568B colour order, but map only the pins used by the drive — leave the unused conductors unterminated at the RJ45 end.
3. Solder the corresponding conductors to a DB9F connector. Match the drive's signal naming to the PC side: drive TxD to PC RxD (DB9 pin 2), drive RxD to PC TxD (DB9 pin 3), signal ground to DB9 pin 5.
4. If hardware handshaking is required, wire drive RTS to PC CTS (DB9 pin 7) and drive CTS to PC RTS (DB9 pin 8), with the loopback strap on the RJ45 side as specified by the original datasheet.
5. Bond the cable shield to the DB9F metal shell (DB9 pin 5 is acceptable as a combined signal/shield ground on the PC side).
6. Strain-relieve both ends with moulded boots or heat-shrink.

Approach B — Active adapter cable with level translation

Use this approach if measurement confirms 0/5 V logic on the RJ45 pins, or if the original cable is known to contain a small PCB at the DB9 end.

1. Build a short adapter pigtail (typically 0.5 m) terminated in an RJ45 plug on the drive side and a small enclosure on the PC side.
2. Inside the enclosure, mount a MAX232 or MAX202 (or equivalent, e.g. Texas Instruments MAX232 datasheet) on a small piece of perfboard. Provide the four 1 µF charge-pump capacitors specified by the IC datasheet.
3. Wire the TTL-level TxD and RxD lines from the RJ45 to the T1IN / R1OUT pins of the level translator. Wire T1OUT to DB9 pin 2 (PC RxD) and R1IN to DB9 pin 3 (PC TxD). Connect ground between the drive, the level translator, and DB9 pin 5.
4. Add TVS diodes (e.g. PESD5V0L1BA or similar) on each line going to the DB9 to provide ESD protection for the PC port.
5. Pot or conformal-coat the adapter board to protect against industrial environments.

PC-Side Configuration

The PC communicates with the S+S Sestep 190/290 using the manufacturer's parameterisation tool. For modern PCs without a built-in RS-232 port, a USB-to-serial converter based on the FTDI FT232 or Silicon Labs CP2102N is acceptable. Industrial-grade converters with galvanic isolation are strongly recommended in panels with VFD switching noise; see the FTDI FT232R product page for a baseline reference design.

If a USB-to-serial converter is used, disable any hardware FIFO or advanced driver options during initial testing. Many converters ship with FIFO enabled by default, which can confuse legacy drive firmware that polls the UART register directly.

Verification Procedure

1. With the drive powered but not in run state, connect the cable. Verify that the drive's service-port LED (if equipped) changes state when the cable is plugged in.
2. Open a terminal program (e.g. PuTTY, Tera Term) at 9600 8N1 with flow control disabled. Press — some firmware revisions emit a banner string on power-up or carriage return.
3. Open the S+S Sestep parameterisation software and attempt a connection. The software should report the drive model and firmware revision within 3–5 seconds.
4. If the software times out, switch the terminal to "local echo" mode and send a known-good query string. A correctly wired cable will echo characters when local echo is on; a cable with crossed Tx/Rx will appear silent.
5. Measure DC voltage between RJ45 pins and ground with the drive powered. Record each pin's voltage in both idle and during attempted communication. Compare against the datasheet reference voltages.
6. If a scope is available, capture the TxD line during a parameter read. A working link shows clean ±5 V to ±12 V transitions; a cable with missing handshaking shows a single burst followed by silence.

Troubleshooting Matrix

Industrial-Grade Cable Sourcing

Engineers looking for ready-made serial programming cables for legacy drives can also evaluate industrial cable suppliers. SEL Cables from Schweitzer Engineering Laboratories is one example of a manufacturer that produces shielded communication cables for industrial and utility environments, with options for custom lengths and connector terminations. While SEL cables are designed primarily for protection and metering equipment, the same construction principles — overall foil + braid shield, tinned copper conductors, oil- and UV-resistant jacket — apply directly to VFD programming cables in harsh environments.

For third-party off-the-shelf RJ45-to-DB9F serial cables, the relevant signal standards are EIA/TIA 574 (DB9 RS-232 pinout) and TIA-568 (RJ45 pinout). Any cable purchased for this application should be documented as a "null modem" or "crossover" configuration only after verifying the drive's signal direction on each pin — a true null-modem cable will not work if the drive is not RS-232 compliant.

Field-Proven Caveats

• Document every pin. Once a working cable is identified, photograph both connector ends and label each wire. Legacy drive pinouts are routinely lost when the original German-language datasheet is misplaced.
• Never hot-plug the RJ45 on a powered drive. Some S+S Sestep 290 variants route 24 V on one of the RJ45 pins for an external keypad. A short to ground through the cable shield will trip the auxiliary supply and may require a power cycle to recover.
• Check for revision differences. The 190 and 290 sub-variants have at least two known hardware revisions. Earlier revisions use a 3-wire TTL interface; later revisions use a 5-wire RS-232 interface with hardware handshaking. Confirm the hardware revision on the drive's nameplate before ordering parts.
• Keep the original cable as a reference. If a donor cable with the small DB9 PCB is available, do not disassemble it. Use it as a reference to probe each signal during initial bench testing.

FAQ