CHAPTER 1 - INTRODUCTION
1.1 FUNCTIONAL DESCRIPTION
The RS-232 Digital Mixing Module (DMM-4DC) 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. 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. 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.
Housed in a sturdy aluminum enclosure and equipped with an internal -48 VDC power supply, the
DMM-4DC will provide in excess of 400,000 hours of reliable service.
DMM-4DC OPERATIONS MANUAL
Page 1
MASTER
REAR VIEW OF DMM-4DC
GND
FRONT VIEW OF DMM-4DC
PWR
E A S T C O A S T
D A T A C O M , I N C .
DMM-4DC
48V
NEG
48V
RET
- +
48V
RET
48V
NEG
PORT 1
PORT 2
PORT 3
PORT 4
RD
SD
1
2
3
4
1
2
3
4
ACTIVE
STREAM
1
2
3
4
SUB-CHANNEL STATUS
ENABLE
DISABLE
