EKF - Short Profile
EKF - Short Profile


XMC Mezzanine Module
Dual Isolated RS-485 Asynchronous Interfaces

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Line Termination


DU1-MUSTANG - Dual Isolated RS-485 Asynchronous Interface
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DU1-MUSTANG • XMC Mezzanine Module

Dual Isolated EIA/TIA-485 Asynchronous Interfaces

The DU1-MUSTANG is a XMC standard single-width mezzanine card, equipped with a PCI Express® to dual-UART bridge. Two 16Mbps RS-485 balanced line transceivers with internal 5kV isolation barrier provide for optimum noise and EMC immunity. The front bezel D-Sub connectors withstand up to 250VAC measured against shield.

The 950-style UARTs (COM ports) are compatible with any asynchronous serial application. Certified device drivers are available for Windows®. The 16Mbps EIA/TIA-485 transceivers can be configured for full-duplex operation (4+1 wire cable) or half-duplex (2+1 wire cable), either point-to-point or multipoint applications.

DU1-MUSTANG • XMC Module • Dual Isolated RS-485

DU1-MUSTANG • XMC Module • Dual Isolated RS-485

The DU1-MUSTANG is equipped with the PLX OXPCIe952 single chip PCI Express® to UART bridge, which is suitable for asynchronous baud rates up to 15Mbps. According to the RS-485 transmission line standard, only the UART receive and transmit data signals are in use, and in addition DTR as RS-485 driver enable control for half-duplex and multipoint configurations.

Two ADM2682E transceivers are provided to meet the RS-485 physical layer specifications. The RS-485 signals of both serial ports are isolated from the board circuitry, and also isolated from each other. Due to the D-Sub connector specification, a maximum of 250VAC between the RS-485 signals measured against shield (front bezel) must not be exceeded.

DU1-MUSTANG - Simplified Block Diagram

DU1-MUSTANG - Simplified Block Diagram
Feature Summary
  • Form factor XMC single-width mezzanine card 139mm x 74mm
  • Stack height 10mm XMC to host
  • Host I/F Connector P15 XMC - PCI Express, single lane, single link
  • Option P15 connector according to XMC 2.0 (white housing)
  • +3.3V operated (VPWR not in use)
  • PCI Express® bridge to dual-port UART
  • PLX Oxford 950 UART w. 128-byte transmit/receive FIFO
  • Asynchronous baud rates up to 15Mbps
  • Windows® & Linux device driver support
  • 5kV rms isolation barrier RS-485/RS-422 transceivers (Analog Devices)
  • Configurable as half or full duplex
  • ±15 kV ESD protection on RS-485 input/output pins
  • Data rate 16 Mbps
  • Connect up to 256 nodes on one bus (driver enable control via DTR)
  • Open- and short-circuit, fail-safe receiver inputs
  • High common-mode transient immunity >25 kV/µs
  • Thermal shutdown protection
  • Two front bezel male 9-pin D-Sub connectors
  • RS-485 ports isolated against each other and board circuitry (limited to 250VAC by D-Sub connector characteristics)
  • On-board DIP-switches for full/half-duplex setting, and line termination on/off
  • Long Term Availability
  • Coating, Sealing, Underfilling on Request
  • RoHS compliant 2002/95/EC
  • Operating temperature: 0°C ... +70°C (industrial temperature range on request)
  • Storage temperature: -40°C ... +125°C, max. gradient 5°C/min
  • Humidity 5% ... 95% non condensing
  • Altitude -300m ... +3000m
  • Shock 15g 0.33ms, 6g 6ms
  • Vibration 1g 5-2000Hz
  • MTBF 121.5 years
  • EC Regulations EN55022, EN55024, EN60950-1 (UL60950-1/IEC60950-1)
subject to technical changes

Ordering Information
Please refer to List 22 for popular DU1-MUSTANG SKUs

DU1-MUSTANG • D-SUB Connectors Pin Assignment

DU1-MUSTANG • D-SUB Connectors Pin Assignment

DU1-MUSTANG • RS-485 Transceiver Line Termination

DU1-MUSTANG • Line Termination

DU1-MUSTANG on a CompactPCI® Serial Carrier Card

DU1-MUSTANG on a CompactPCI® Serial Carrier Card

Is RS-485 a two-wire ore a three-wire system? It is most definitely a three wire system (four plus one wire with respect to full-duplex operation). The TIA standard (ANSI/TIA/EIA-485-A, page 15, A.4.1) requires the presence of a common return path between all circuit grounds along the balanced line for proper operation.

The TIA standard defines a maximum common mode voltage range from -7V to +12V on the signal lines A and B, measured against C (common ground). A TIA/EIA-485 system however with only two wires A and B (C generator and C receiver commons not connected) can result in an unpredictable common mode voltage superimposed on the interface lines A and B, caused either by electrostatic charging or electromagnetic interference.

A 2-wire system often may work though due to idle-line fail-safe resistors at the receiver inputs, which can be considered as a loosely coupled common ground. Nevertheless this operation mode cannot be recommended - what is working flawless in the laboratory may not work reliable under real conditions in an industrial environment.

Where do we get the third wire? Many times the outer cable shield is used as the third (fifth) wire. However, EKF recommends to use a two pair cable (three pairs for full-duplex operation), with one or both wires of the additional pair as the dedicated common ground. Connect these additional wires directly to the pins 3, 6 & 5, 8 of the DB9 connector for proper grounding.

The optimum cable solution would comprise an inner shield for each signal twisted pair. The inner shield can then be used for establishing the common ground between TIA/EIA-485 nodes (connect to pins 3, 6 & 5, 8 of the DB9 connector).

An additional outer cable shield, that may cover the inner signal and ground cable pairs, should be connected to the pin 1 of the connector (it is equivalent and sufficient to connect the shield with the metallic shell of the DB9 connector). This shield should be grounded at one point only (isolate the shield at the opposite cable end in order to avoid any contact with the connector hood).

You may read a helpful article related to this topic.

Interconnect Application According to ANSI/TIA/EIA-485-A

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