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Features / Benefits

* Interface - EIA RS-232, CCITT V.24, DB-25 Female Connectors

* Data Rates - Synchronous or Asynchronous up to 64Kbps

* Anti-Streaming - Automatic or Manual for unattended Circuit Restoral

* Individual Subchannel
Enable/ Disable Switches

* Visual Indication of Subchannel Activity

* Receive Data - Broadcast to all Subchannels

* Transparent to Data

* Fully Cascadable

* External Clocking

* Sturdy Metal Enclosure

* 110/220VAC Switch Selectable

* +/- 15KV ESD Protection



The MSD-4, PT# 101012 RS-232 Modem Sharing Device provides the network manager with a cost effective means of expanding existing, leased line polled networks without adding computer ports or communications links. With the MSD-4, up to four terminals can share the same port and communications link using the contention and control protocols normally resident in the host hardware and software. 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 MSD-4 is protocol transparent at data rates up to 128Kbps. Data arriving at the Master Port is continually broadcast to all Subchannels. The attached terminal device that raises the RTS control signal is automatically given control of the MSD until data transmission is complete. Clocking is accomplished from the attached Modem.

The MSD-4 incorporates optional Anti-Streaming circuitry. If enabled, Anti-Streaming will automatically remove a defective terminal 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 MSD-4 will provide in excess of 100,000 hours of reliable service.

The MSD-4 have a 3-year warranty and a 24 hour turnaround on warranty repairs.

MSD-4 Diagram



Multiple sync/async terminal or DTE devices operating in a polled environment, to share one Modem

Capacity One to four RS-232 Sync/Async devices

EIA RS-232, CCITT V.24 using DB-25 female connectors


Data Rates Up to 64Kbps
Data Format

Data transparent at all data rates


External; from attached Modem


OR-MODE (Switch on Data)

Anti-Streaming Automatic…Selectable time out intervals
Disable……Selectable via dip switch
Terminal Service Modes Rotational sequence for equal access
Priority Mode Optional
Front Panel

Indicators: Power, CTS, DCD, RXD, TXD
Channel Active
Switches: Enable/Disable of each Sub-channel

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

MSD-4 PT# 101013
Height ....... 2.53 inches (6.426 CM)
Width ........ 12.13 inches (30.810 CM)
Length ....... 11.13 inches (28.270 CM)
MSD-4 PT# 101030
Height ....... 1.75 inches (6.426 CM)
Width ........ 17.00 inches (43.180 cm)
Length ....... 11.50 inches (29.210 CM)

6 pounds (2.72Kg)

Warranty Three Years, Return to Factory
MTBF 601,328 Hours
Benign Ground, Controlled, Telcordia Issue 1
Approvals EMI Approvals
FCC 47CFR, Part 15, Subpart B for conducted emissions from a Class A
FCC 47CFR, Part 15, Subpart B for radiated emissions from a Class A
Safety Approvals UL 62368-1: 2014
Electric Discharge Approval IEC EN-61000-4-2
Environmental Testing Approvals Operating Temperature: 50º to 160º F (10º to 60º C)
Operational Alt.: 0 to 10,000 feet above sea level
Operational Relative Humidity: 10% to 80%
Non-Operational Temperature: -30 degC to 70 degC
Non-Operational Alt.: 0 to 50,000 feet above sea level
Ordering Information

PT# 101012
Model: MSD-4
Description: 4-Port RS-232 Sharing Device, Standalone

PT# 101030
Model: MSD-4
Description:  4-Port RS-232 Sharing Device, 1U Rackmount

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
Optional Accessories 1) Spare Data Center Fuses
A) 160ma Fuse, Qty (2) Part # 714000
B) 80ma Fuse, Qty (2) Part # 714001