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dc power port sharing device

Features / Benefits

  • RS-232 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
  • -36 to -72 DC Input


The RS-232 Digital Mixing Module (DMM-4DC) or port sharing device is a network expansion device for modem sharing or port sharing applications in polled or contention environments. The DMM-4DC allows up to four devices to share a modem / DSU or computer port. The port contention modes are RTS, DCD or switch on Data. Any combination of terminals and modems may be used in a network environment. Each port of the DMM-4DC 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-4DC is protocol transparent at data rates up to 128Kbps. The DMM-4DC may be configured to provide clocking for the entire network. To prevent data transmission errors caused by clock differentials throughout a synchronous network, a 8 bit ring buffer is provided for re-synchronization. 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 (CTS) control signal is not provided by the master port, an option for forced CTS is available via 3-position stick headers. Additionally, several user defined RTS/CTS delay settings are available.

The DMM-4DC also 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.

The DMM-4DC is housed in a sturdy aluminum standalone or rackmount enclosure The unit is equipped with an internal -48 VDC power supply and will provide in excess of 315,419 hours of reliable service. All RS-232 data ports and the power supply have surge protection that utilize Sidactors

port sharing device application diagram


Application Multiple Sync/Async DCE/DTE devices operating in a polled or contention environment, to share one DCE/DTE port
Main Input: One RS-232 Port Subchannel Ports: One to Four RS-232 Sync/Async devices Main Input: One RS-232 Port Subchannel Ports: One to Four RS-232 Sync/Async devices
Interface EIA RS-232-D, CCITT V.24 using DB-25 female connectors, selectable as DCE or DTE interface
Data Format Data transparent at all data rates
Data Rates Internal Select: 450bps to 76.8Kbps External: Up to 128Kbps
Timing Options Internal
External: via Input Master Port
External: Telco Timing via Port 1
Automatic: Selectable time-out intervals
Disable: Selectable via dip switch
Terminal Service Modes Sequential scanning for RTS or DCD control signal, option for switch on RXD Data(JP6-JP9)
Clear To Send Allows normal RTS/CTS handshaking or has option for Forced CTS on Ports 1-4 (JP1-JP4)
RTS To CTS Delay Selectable RTS to CTS delays of 0, 5, 10 and 20ms
Front Panel Indicators: Power, Transmit Data, Receive
Data, Channel Active, Channel Stream
Switches: Enable/Disable of each Sub-channel
Power Source DC Voltage, Input Range of -36 to -72vdc Current Draw at 48vdc: 75ma @ 3.6watts
Regulatory  Approvals Tested According to

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

CE Safety EN60950 and CE EMC EN300-386-2
MTBF 315,419
Telecordia Issue 1
Operating Temperature:
32º to 122º F (0º to 50º C)
Relative Humidity:
5 to 95% Non-Condensing
Altitude: 0 to 10,000 feet
Dimensions DMM-4DC
Height: 1.75 inches (4.44 cm)
Width: 17.00 inches (43.18 cm)
Length: 9.00 inches (22.86 cm)
Weight 4.5 pounds (2.1Kg)
Warranty Three Years, Return To Factory
Ordering Information Part Number: 162000
Model: DMM-4DC
Description: RS-232 Digital Mixing Module

Included with each unit:
1) Operations Manual
2) Rackmount Kit

Optional Accessories
315ma Fuse, Qty (2) Part # 714004