Siemens 6ES7972-0BB50-0XA0 PROFIBUS DP Bus Connector – SIMATIC S7-300

Siemens 6ES7972-0BB50-0XA0 — PROFIBUS DP Bus Connector in the S7-300 Fieldbus Architecture

The 6ES7972-0BB50-0XA0 is a passive PROFIBUS DP bus connector manufactured by Siemens AG for use within the SIMATIC S7-300 and ET 200M distributed I/O ecosystem. Its primary function is to terminate and pass through the RS-485 differential signal pair at each node on a PROFIBUS DP segment, while simultaneously providing an isolated programming/monitoring port that allows a PG/PC to access the bus without interrupting live communication. This combination of bus-through and diagnostic-access capability makes it a structurally significant component in any multi-node PROFIBUS DP installation.

In a typical S7-300 control loop, the CPU module acts as the DP master. It polls each slave node — ET 200M remote I/O racks, SINAMICS drives, SIRIUS motor starters, or third-party DP slaves — within a fixed, configurable bus cycle. The 6ES7972-0BB50-0XA0 connector sits at the physical layer of this loop: it receives the incoming bus cable, routes the differential pair to the device’s DP port, and passes the signal onward to the next node. At segment endpoints, its on-board switchable termination network (a 390 Ω pull-up to VP, a 220 Ω line terminator, and a 390 Ω pull-down to DGND) absorbs signal reflections that would otherwise corrupt data frames at baud rates above 1.5 Mbit/s. Correct termination is not optional at 12 Mbit/s — without it, reflected waveforms overlap the next transmitted frame within the 83 ns bit period, causing CRC errors and forcing the master to retransmit, which directly degrades the deterministic cycle time that PROFIBUS DP guarantees.

The 90° cable exit geometry is a deliberate mechanical design choice. In DIN-rail-mounted S7-300 racks installed inside standard 19-inch or 600 mm-wide control cabinets, horizontal cable exits from the CPU’s DP port would require a minimum bend radius that conflicts with adjacent modules or the cabinet door. The vertical 90° exit routes the PROFIBUS cable upward or downward along the DIN rail, keeping the cable bundle parallel to the rack and within the cable duct without exceeding the cable’s minimum bend radius of 35 mm (for standard PROFIBUS Type A cable). This reduces mechanical stress on the cable shield termination and maintains shield continuity — a factor that directly affects EMC performance at high baud rates.

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Technical Parameters

Hardware Logical Analysis

The internal circuit of the 6ES7972-0BB50-0XA0 is built around three functional blocks that operate independently of any external power supply, drawing only from the bus VP line (+5 V, pin 6) when termination is enabled.

Termination Network Logic: The switchable termination consists of a three-resistor network: a 390 Ω resistor between VP (pin 6) and line A (pin 3), a 220 Ω termination resistor between lines A and B, and a 390 Ω resistor between line B (pin 8) and DGND (pin 5). This network matches the 150 Ω characteristic impedance of PROFIBUS Type A cable (the 220 Ω resistor in parallel with the cable’s distributed impedance yields the correct termination). The switch physically disconnects the VP and DGND connections, not the 220 Ω resistor — meaning the termination is only active when the bias resistors are also connected, preventing a floating 220 Ω load from distorting the idle-state bus voltage. This design prevents a common installation error where a termination resistor is left connected without bias, which can pull the differential voltage below the 200 mV threshold required for reliable idle-state detection.

PG Port Isolation Architecture: The integrated PG/PC port is a passive electrical tap on the bus lines, not an active repeater. It presents a high-impedance load to the bus — within the PROFIBUS specification of 32 unit loads per segment — so connecting a PG/PC for online diagnostics does not alter bus loading or timing. The tap is always active regardless of the termination switch position, allowing a technician to monitor bus traffic with a PROFIBUS analyzer at any node without reconfiguring the segment.

EMC Shield Termination: The connector housing provides a direct low-impedance path from the cable shield (connected at the cable clamp) to the Sub-D shell, which in turn connects to the device chassis ground through the mating connector. This single-point shield termination at each node, combined with the cable’s foil-and-braid shield, achieves a shield transfer impedance below 10 mΩ/m at frequencies up to 30 MHz — sufficient to suppress common-mode interference from variable-frequency drives and switching power supplies operating in the same cabinet. The 90° cable exit geometry ensures the shield clamp engages the cable at a mechanically stable angle, preventing the shield from being pulled away from the clamp under cable weight or vibration.

System Integration Benefits

• Zero-downtime diagnostics: The integrated PG port allows a STEP 7 or TIA Portal session to connect to any node on the segment without removing the bus connector or interrupting the running DP cycle — critical for fault diagnosis on 24/7 production lines.
• Deterministic cycle time preservation: Correct on-board termination eliminates signal reflections that force the DP master to invoke error recovery routines, keeping the bus cycle within the configured watchdog timeout and preventing spurious slave failures.
• Simplified segment commissioning: The switchable termination removes the need to stock and install separate termination plugs at segment ends, reducing the number of distinct spare parts and eliminating the risk of incorrect external termination values.
• Mechanical compatibility with S7-300 rack geometry: The 90° exit fits the physical envelope of a fully populated S7-300 rack (up to 11 modules) without requiring additional clearance in front of the CPU DP port, enabling higher module density in compact cabinets.
• Full baud-rate range support: A single connector model covers all PROFIBUS DP baud rates from 9.6 kbit/s to 12 Mbit/s, eliminating the need to select different connector variants for different network speeds during system expansion.
• Reduced wiring error risk: The Sub-D 9-pin interface is keyed and polarized; incorrect insertion is mechanically prevented, eliminating the wiring polarity errors (A/B line reversal) that are a common source of PROFIBUS commissioning failures.
• Long-term spare parts availability: The 6ES7972-0BB50-0XA0 has been in continuous production within the SIMATIC S7-300 lifecycle and is stocked globally, ensuring replacement availability for installed bases with 10–20 year operational horizons.
• Interoperability with all PROFIBUS DP device classes: As a passive connector compliant with IEC 61158, it operates with any DP master or slave regardless of manufacturer — Siemens, ABB, Beckhoff, Phoenix Contact, or third-party devices — without configuration changes.
• Reduced cabinet heat load: The passive design draws no additional current from the control cabinet power supply (termination network draws ≤ 50 mA from VP only when enabled), contributing no measurable thermal load to the cabinet thermal budget.

Quality Assurance & Global Logistics

Every unit of the 6ES7972-0BB50-0XA0 supplied by siemensplc.com is sourced as genuine Siemens original product. Each shipment undergoes a structured pre-dispatch verification protocol:

• Authenticity verification: Siemens holographic security labels, date codes, and factory packaging seals are inspected against current Siemens authentication standards before any unit is allocated to an order.
• Electrical continuity check: Pin continuity across all nine Sub-D contacts (device port and PG port) and shield-to-housing resistance are measured and logged for each unit.
• Termination switch function test: The on-board termination switch is cycled and the resulting impedance change on lines A and B is verified against the 220 Ω ± 5 % specification.
• ESD-safe packaging: Units are individually sealed in anti-static bags, placed in foam-lined cartons, and outer-packed with moisture-barrier desiccant for long-haul air freight.

Shipments originate from our warehouse in Xiamen, China. Standard air freight transit times are 3–7 business days to Europe and North America, 2–5 business days to Southeast Asia and the Middle East. DHL Express, FedEx International Priority, and UPS Worldwide Express are the primary carriers. Full export documentation — commercial invoice, packing list, certificate of origin, and ECCN classification — is prepared for every international shipment. Urgent same-day dispatch is available for orders confirmed before 14:00 CST.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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