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4
THEORY OF OPERATION AND APPLICATIONS
4.1 INTRODUCTION
This chapter contains a simplified functional description of the RSD-20, and covers the flow of
data, controls and clocks in all RSD-20 operating modes.
4.2 CONTENTION
RTS/DCD contention in V.35 interface is interchangeable with CONTROL/INDICATION
contention for X.21 interface. Sub-channel access to the main channel for data transmission is
controlled by RTS/DCD (Request to Send/Data Carrier Detect) or (CONTROL/INDICATION in
X.21 version) or data contention. When selected, the data and timing signals of the active
sub-channels pass through the contention circuit and the SELECT/DESELECT circuit of the
sub-channels to the elastic buffer, where data is clocked in and out of the main channel.
When a continuous mark is detected, and if strapped to data contention, the
SELECT/DESELECT circuit breaks the data path of the active sub-channel. It then selects
another sub-channel and resets the buffer. Otherwise the sub-channel will remain connected
until RTS/DCD or (CONTROL/INDICATION) go down.
4.3 SUB-CHANNEL DISABLE
Manual or automatic disable of streaming sub-channels is possible. If the sub-channel is DTE
(connected to a modem) the RSD-20 drops RTS, and if the sub-channel is DCE (connected to
port) the RSD-20 drops DCD and CTS and X.21 drops CONT. In addition, the RSD-20 will stop
transmitting data to the sub-channel, and will ignore any data received from it.
4.3.1 Manual Disable
Manual disable is activated by four push-button switches, one for each sub-channel, which are
located on the front panel. Disabling the sub-channel is achieved by depressing the appropriate
switch. The sub-channel will remain inactive until the switch is released by depressing it again.
4.3.2 Automatic Disable
A streaming sub-channel is disabled automatically if it has stayed active for longer than a preset
period of time, thereby blocking all other sub-channels. Automatic disabling of a sub-channel
resets itself each time RTS/DCD or data (in data contention mode) drops. Selection of one of
three different time delays or non-active mode as indicated on the PCB.
RSD-20 OPERATOR'S MANUAL THEORY OF OPERATION AND APPLICATIONS
4.4