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CHAPTER 5: Operation
the local DTE by the loop control block within the processor. Any data present on
the line or at the far-end DTE interface is invalid. The remote unit will remain in
the startup mode, NS LED on, CTS LED yellow, and CD LED yellow, until the local
unit is taken out of the local loop mode. After the local loop is deselected, the
units will both be in startup mode and the link will be established.
Figure 5-3. Local loop mode 1.
A mode 2 local loop is shown in Figure 5-4. When the local loop is initiated, either
by the front-panel switch or the DTE interface, two separate loop paths will be
started. In the first path, data presented to the local DTE interface will be looped
back to the local DTE within the framer. In the second path, data presented at the
far-end DTE will be transmitted to the local DTE and then looped back within the
local DTE loop control block with the processor. After the local loop is deselected,
the units will be placed back into data mode and the normal data paths will be re-
established.
Figure 5-4. Local loop mode 2.
