Located on the rear panel of the product are the RS-232 user data ports and the -48VDC input
connector.
2.3 CLOCKING, INTERNAL AND EXTERNAL
Three modes of clocking are available to the DMM-4DC user.
1) Clocking may be set as Internal Timing utilizing the internal Baud Rate Generator.(JP5,
connect 1 and 2)
2) Clocking may be set as External Timing utilizing a DCE device attached to the Master Port
.(JP5, connect 2 and 3)
3) Clocking may be set as Telco Timing from an attached DCE via Port 1 .(JP5, connect 2 and 4)
Internal Timing mode will facilitate user defined operational speeds from 450bps to 76.8Kbps.
Networks such as 56/64k DDS (Digital Circuits) should be timed via Port 1.
A Green LED illuminates when DC Power has been applied. Two adjacent Green LEDs
illuminate in union with individual Green subchannel port activity LEDs and identify Transmit
and Receive data transmissions. Yellow LEDs provide the user with a visual indication of a
streaming DTE (ref. 2.6) Positive latching switches are provided for each DTE port for isolating
or removing a streaming terminal. Each DTE port has its own switch and operates
independently. To disable a subchannel, simply push the switch. A channel is disabled when the
switch is in the outer most position.
2.2 REAR PANEL CONNECTORS
CHAPTER 2 - BASIC OPERATION
2.1 FRONT PANEL INDICATORS AND SWITCHES
1.2 THEORY OF OPERATION
The DMM-4DC allows up to four DCEs or DTEs to share one DCE or DTE communications
link. In a broadcast, polled or contention environment, the typical DMM-4DC operation is as
follows:
Data arriving at the DMM-4DC's master port is continually broadcast to all subchannel ports.
When one of attached DCE or DTE devices answers a poll from the host site, that device will
raise RTS (Request To Send for terminals) or DCD (Data Carrier Detect for modems). When
RTS or DCD is raised, the DMM-4DC will lock on to that port and allow that device to
communicate to the Host Site. The DMM-4DC will remain locked onto that port until RTS or
DCD is dropped. After RTS or DCD has dropped, the DMM-4DC will automatically begin
scanning the ports until another port raises RTS or DCD.
