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.