Siemens 6NH7701-5AN RS232 Cable Pinout for SINAUT TIM to MD720-3

Overview

The Siemens 6NH7701-5AN is a factory-assembled RS232 connecting cable designed for the SINAUT ST7 telecontrol system. It links a TIM (Telecontrol Interface Module) — the SINAUT front-end for SIMATIC S7-300 and S7-400 stations — to a Siemens GSM/GPRS modem, specifically the legacy MC45T terminal or the current MD720-3 industrial modem, using a standard EIA-232 (RS232) interface. The 2.5 m cable is pre-terminated and can also be deployed with any third-party modem or radio device that exposes a true RS232 port, eliminating the need for field fabrication in a control cabinet.

The cable is built around a 1:1 straight-through DB9 male-to-DB9 male wiring scheme, with the transmit and receive pairs crossed at the OEM connector ends so that the TIM (DTE) sees the modem (DCE) on its COM port. Each end uses a right-angle metal back-shell to fit inside the limited depth of a TIM module or the MD720-3 housing; users who prefer axial connectors must source a generic 9-pin straight-through cable and verify the pin mapping.

Cable Specifications

DB9 Pinout Reference

Both connectors follow the standard EIA-232 DB9 pin assignment used on industrial PCs, SIMATIC TIMs, and the MD720-3 modem. A compact signal reference is provided in the SIMATIC S7-1200 Communication Interfaces technical specifications and applies identically to the TIM family.

Internal Wiring of the 6NH7701-5AN

The cable is wired as a 1:1 straight-through link between the two DB9 connectors. The signal ground and shield are tied together to provide a common reference for the unbalanced RS232 drivers.

RS232 Signal Levels and Timing

RS232 uses unbalanced, single-ended signaling with respect to signal ground (pin 5). The Siemens TIM and MD720-3 both implement compliant drivers per EIA/TIA-232-F and CCITT V.28.

The SINAUT protocol stack (SINAUT ST1, ST7, or SINAUT TIM firmware) typically runs the RS232 port at 19.2 kbit/s or 57.6 kbit/s with 8 data bits, no parity, and one stop bit (8N1). The MD720-3 also supports 115.2 kbit/s for higher throughput on GPRS sessions, but the application layer in the TIM dictates the effective throughput.

Application Context — SINAUT ST7

SINAUT ST7 is the Siemens telecontrol protocol that runs on S7-300/S7-400 PLCs equipped with a TIM module (e.g., TIM 3V-IE, TIM 4R-IE, TIM 3V-IE DPN). The TIM encapsulates process data into SINAUT frames and forwards them over a WAN — historically analog/digital radio or dedicated line, but in modern installations GSM/GPRS via the MD720-3.

The 6NH7701-5AN supplies the physical transport between the TIM's RS232 port and the modem. From the S7 CPU's perspective, the TIM appears as a CP (communications processor) on the backplane, and the WAN link is transparent. Configuration is performed in STEP 7 / TIA Portal under the TIM's "Modem" properties, where the COM port parameters (baud rate, data bits, parity) must match the modem defaults.

Compatible Modems and Devices

The cable is qualified for the following devices. Third-party radios, satellite terminals, and industrial routers can be substituted provided they expose a true RS232 DCE port (not a 3.3 V logic UART).

Connection Topology

Mechanical and Installation Notes

1. Connector orientation. The right-angle back-shells keep the cable parallel to the front face of the TIM and MD720-3, allowing DIN-rail mounting in 150 mm-deep cabinets. Do not force the connector — keyed shells prevent reversal.
2. Strain relief. Use the integrated screws on the DB9 back-shells (2-56 UNC thread) to secure to the TIM and modem chassis. Torque to 0.3 N·m.
3. Shield termination. The drain wire / braided shield is bonded to the metal back-shell on both ends. In plants with high common-mode noise, bond the shield to cabinet ground at one end only and use a short pigtail (≤ 25 mm) to avoid ground loops.
4. Bend radius. Maintain a static bend radius of ≥ 30 mm and a dynamic radius of ≥ 60 mm. Repeated flexing below these values will fatigue the conductors.
5. Maximum run. RS232 specifies a maximum cable length of 15 m at 19.2 kbit/s, limited by the 2500 pF distributed capacitance. The 2.5 m 6NH7701-5AN has margin to spare; do not extend with a passive coupler without re-checking capacitance.

Commissioning and Verification

1. Power down the TIM and the modem before mating the cable. Hot-plugging RS232 lines is generally tolerated by modern transceivers, but cold-plugging protects against inrush on the +24 V supply rail.
2. Hand-tighten the DB9 retaining screws on both ends.
3. Apply 24 V DC to the TIM and the modem. The MD720-3 will begin its boot sequence; the green "PWR" LED should be steady within 8 s.
4. In STEP 7 / TIA Portal, open the TIM's "Diagnostics" tab. The "Modem" status field should report "Modem ready" or "Modem connected" within 30 s, indicating DSR and DCD are both asserted.
5. Issue an AT-command test from the TIM console: AT should return OK. Then AT+CSQ reports signal strength (0-31, with ≥ 10 considered acceptable).
6. Initiate a SINAUT test frame. In the SINAUT ST7 toolbox, select "Send test telegram" to the control center. A successful response confirms TD/RD, RTS/CTS, and DTR/DSR handshaking.

Troubleshooting Matrix

Substituting Third-Party or Field-Fabricated Cables

Although the 6NH7701-5AN is a turnkey item, an integrator may need a field build when stocking spares is impractical. A working substitute can be assembled from:

• Two DB9 male solder-cup connectors with metal back-shells (e.g., AMP 747905-2 or equivalent).
• 7-core shielded cable, 26 AWG stranded, 30 V rated, overall foil + braid.
• Heat-shrink boots at each connector for strain relief.

Wire 1:1 per the table above, ensure the drain wire is clamped under the back-shell at both ends, and shrink the boots before the cable is installed. For SINAUT TIM → PC diagnostic links, the standard Siemens PC-configuration cable wiring for other Siemens peripherals uses a similar straight-through convention, but always verify the modem and DTE roles before assembling.

Compliance and Standards

The cable's electrical performance aligns with:

• EIA/TIA-232-F — Interface between Data Terminal Equipment and Data Circuit-Terminating Equipment employing Serial Binary Data Interchange.
• CCITT V.28 — Electrical characteristics for unbalanced double-current interchange circuits.
• IEC 61131-2 — Industrial process measurement and control — programmable controllers — equipment requirements (EMC, ESD ±4 kV contact / ±8 kV air).

When deployed inside a control cabinet with proper segregation from VFD output cables, the link will satisfy EN 61000-6-2 (industrial immunity) and EN 61000-6-4 (industrial emissions) under the SIMATIC system's CE declaration.

FAQ