RS-232 Port Sharing Device

Asynchronous or Synchronous Port Sharing Device - Ideal for Modems or SCADA

  • Synchronous or asynchronous data
  • 6 ports, RS232 up to 256 Kbps
  • Data is broadcast from composite to all ports
  • Port to composite is RTS/CTS controlled
  • Logical "OR" to composite without RTS control is an available option
  • Active drivers and receivers for extended cable lengths
  • Units can be concatenated for 11, 16, 21 or more ports
  • RTS/CTS port selection takes less than 1 ms
  • Anti-streaming option


Physical and Electrical




The MSU-6 is a port sharing device ( MSU ) designed for sharing one RS232 link with multiple DTE devices. The composite or DCE port of the MSU is typically accessed by RTS control. The MSU-6 can be modified to logically "OR" the 6 ports to the composite. The devices can be synchronous or asynchronous. The interface is RS232, up to 256 Kbps. All data from the composite, or common channel, is broadcast to all 6 ports. Data from the ports to the composite is sent only from the port that has asserted RTS and has received CTS back from the composite port. Ports are scanned at a sub-millisecond scan rate.

If more that 6 ports are needed, additional MSU-6s may be concatenated. Each additional MSU-6 adds 5 more ports, since one port is given up on the primary unit to support the addition of 5 more ports. Concatenating MSU-6 units adds virtually no delay to the system, as switching is done in less than a millisecond, even when concatenated several units deep.

The MSU has active drivers and receivers on all ports. This insures that the unit exceeds the RS232 minimum cable distances. For example, the RS232 standard for 19,200 bps data is 50 feet of cable. With the active drivers and receivers, users often run cables in excess of 100 feet at 19,200 bps data rates.

When used as a synchronous device, the attached DCE device must be a source of clocking.

The MSU-6 has front panel LED's that show port activity for each port. On the composite, or common channel, there are LED's for Transmit Data, Receive Data and Clear to Send. There is also a power indicator.

Normally used to share one DCE port amongst multiple DTE ports, the MSU may be used in the reverse direction. To share a single DTE port amongst multpile DCE ports, such as broadcasting asynchronous data, see our Asynchronous Sharing Unit, the ASU. The ASU is available in 4, 8, 16, 24, and 32 port units. The data sheet is here.

Controls and Indicators
Physical and Electrical

Typical Applications

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Item Number Description Price Buy Now!
MSU-6 6 Port, Port Sharing Unit w/ 120VAC Power Supply $ 525 Qty:
9902099 Rack mount 2-U high 19" wide $ 60 Qty:
9501040Optional 12 VDC (9-18 VDC) power supply in place of standard power supply $ 75 Qty:
9501031Optional 24 VDC (19-36 VDC) power supply in place of standard power supply $ 75 Qty:
9501044Optional -48 VDC (36-72VDC) power supply in place of standard power supply $ 75 Qty:
950130Optional 125 VDC power supply in place of standard power supply $ 125 Qty:

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