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Port Sharing Device product picture

Features / Benefits

  • Port Sharing Device
  • Interface - EIA RS-232, CCITT V.24, DB-25 Female Connectors
  • Data Rates - Synchronous or Asynchronous to 128Kbps
  • Anti-Streaming - Automatic or Manual for unattended Circuit Restoral
  • DCE/DTE Selectable
  • Tail Circuit Buffer
  • Supports CSU/DSU's, LL Modems, Dial Modems and Terminals
  • RTS/CTS delays options
  • Transparent to Data
  • Fully Cascadable
  • Internal or External Clocking
  • Sturdy Metal Rackmount Enclosure<
  • 110/220VAC Switch Selectable


The RS-232 Port Sharing Device (DMM-4) is a network expansion device for modem sharing or port sharing applications in polled or contention environments. The DMM-4 allows up to four devices to share a modem/DSU or computer port. Any combination of terminals and modems may be used in a network environment.

Each port of the DMM-4 may be selected as a DCE or DTE interface.

Once installed, system and network efficiency are increased through higher host processor utilization coupled with the significant decrease in idle time between host / terminal traffic sessions.

Ideal for either synchronous or asynchronous network environments, the DMM-4 is protocol transparent at data rates up to 128Kbps. The DMM-4 may be configured to provide clocking for the entire network. To prevent data transmission errors caused by clock differentials throughout the network, an 8 bit buffer is provided. In applications where the master port and the selected port provide their own clocks, data is clocked into the buffer at the receive clock rate of the active port and clocked out using the master port transmit clock.

In applications where the Clear To Send control signal is not provided by the master port, an artificial RTS/CTS is available. Additionally, several RTS/CTS delay settings are available.

The DMM-4 provides optional Anti-Streaming circuitry. Once enabled, Anti-Streaming will automatically remove a defective terminal or modem from service if the Data / Control criteria is present for the user predefined selection period.

Housed in a sturdy metal enclosure and equipped with an internal 110/220VAC switch selectable linear power supply, the DMM-4 will provide in excess of 100,000 hours of reliable service.

The DMM-4 has a three year warranty and a 24 hour turnaround on warranty repairs.

RS232 Port Sharing Device application diagram


Application Multiple Sync/Async DCE/DTE devices operating in a polled, contention, or dial environment, to share one DCE/DTE port
Capacity One to four RS-232 Sync/Async devices
Interface EIA RS-232, CCITT V.24 using DB-25 female connectors
Data Format Data transparent at all data rates
Data Rates Internal: Up to 76.8Kbps
External: Up to 128Kbps
Timing Internal or External
Anti-Streaming Automatic....Selectable time out intervals

Disable........Selectable via dip switch

Terminal Service Modes Sequential scanning for RTS, DCD or Data
 Front Panel Indicators....Power, Transmit Data, Receive Data, Channel Active, Channel Stream

Switches.....Enable/Disable of each Subchannel

Power Source 100-120 to 200-220VAC @10%, 50/60Hz, 0.16/0.08A, external 110/220 volt select switch, IEC Power Inlet, (2) 5mm Fuses
Regulatory Approvals Tested According to

UL 60950-1:2003, CAN/CSA-C22.2 No. 60950-1:2003

FCC Part 15, Class A
Environmental Operating Temperature . .32º to 122º F (0º to 50º C)

Relative Humidity.. . . . . . .5 to 95% Non-Condensing

Altitude. . . . . . . . . . . . . ... .0 to 10,000 feet


DMM-4 (Rackmount Model)

Height ....... 1.75 inches (4.44 cm)

Width ........ 17.00 inches (43.18 cm)

Depth ....... 9.00 inches (22.86 cm)

Weight 4.5 pounds (2.1Kg)
Warranty Three Years, Return to Factory
Ordering Information: Model: DMM-4
Description: RS-232 four port Digital Mixing Module
Included with each unit: 1) Operations Manual

2) U.S.A. Grounded Power Cord, Part # 713015

3) Optional Power Cords

....A) United Kingdom, Part # 713016

....B) Continental Europe, Part # 713017

....C) Other: Specify Country on Purchase Order


1) Spare Data Center Fuses

....A) 160ma Fuse, Qty (2) Part # 714000

....B) 80ma Fuse, Qty (2) Part # 714001