The TMUX rack-mount unit (see Figure 1) provides 12 channel telemetry multiplexing and demultiplexing over standard DS2 links (6.2 Mbps). Each unit can act as one side of a bidirectional link, both multiplexing 12 independent channels into a DS2 stream on one side, and also demultiplexing 12 independent channels from the DS2 stream on the other side. Channel data is input and output as differential lines for clock and for data. At the demultiplexer output, the clock jitter is held below 1%, permitting the use of bit synchronizers on just the data line. Each channel can be configured to any rate between 10 Hz and 6 MHz.

Figure 1. TMUX Rack-Mount Unit

The TMUX can be controlled by either manual control of the front panel keypad (with readout from the LCD display), or by RS-232 for remote operation. Automatic forwarding of alarm messages further supports remote operation. Control parameters include specifying whether DS2 framing bits are to be included for the multiplexer and for the demultiplexer (they can be independently configured). It is not necessary that two units be attached together, but instead they could be daisy-chained with additional units.

Nominal channel data rates can be user configured, with the TMUX constraining operation to within 10% of the nominal data rate. Each channel can also be configured for automatic frequency configuration, whereby the unit measures the input data rate and re-configures the nominal rates without user intervention. In this manner, the unit can be setup once and never needs to be adjusted for changing channel rates.

Figure 2. TMUX Unit Block Diagram

Figure 2 presents a block diagram of the TMUX unit. Independent channels of clock and data are loaded into the Input FIFOs. The MUX combines the FIFO contents into packets spanning all 12 channels, and the serial data is then sent to a DS2 line driver. The resultant signal meets the DS2 electrical requirements, and can drive 1’ to 300’ of cable. A separate DS2 input goes into the line receiver, sending the serial stream to the DEMUX. The DEMUX demultiplexes the channel data from the incoming packets, sending the data to the Output FIFOs, and sending rate information to the clock regenerators. The regenerated clocks drive the parallel-to-serial circuitry, resulting in 12 output channels of smoothed, differential clock and data lines. The front-panel as well as the remote control RS-232 lines supply configuration to the MUX, which can then pass on information to the DEMUX. Status information goes in the reverse direction.

The TMUX unit measures 8 ¾" x 17 ½" x 22 ½", and is intended for rack-mounting. It includes side-to-side airflow driven by internal fans, and includes an overtemperature alarm. The unit is powered by 200 W of 110 VAC.

If you are interested in further details, please contact Doug Leepa at Veridian Systems, Inc. (dleepa@veridiansystems.com).

Last modified: 21 August 1999