CANOGA PERKINS 2270 Fiber Optic Modem - Manual (Page 52)

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Canoga Perkins
If Data Carrier Detect (DCD) is present as an interface output, it is asserted if the remote modem
is sending valid optical carrier to the local modem. If the interface is looped back for testing, DCD
is asserted, regardless of the state of optical carrier. However, when Flow Control Mode is active,
the loopback forces DCD to follow the Request To Send (RTS) signal.
Clear To Send (CTS) is handled entirely by the interface card. Typically, CTS will follow the state of
RTS with some delay between the time RTS turns on and CTS turns on. Some interfaces may
interlock CTS with the presence of receive optical carrier through the DCD signal.
4.8.1 Flow Control
The only form of end-to-end flow control available will allow RTS at the near end to control DCD on
the far end. This feature is enabled by the selection of Flow Control Mode. (Closing switch position
7 of the eight-section switch bank on the front panel selects Flow Control Mode.) Once enabled,
this flow control will also stop any data transmission in the direction of the signaling if the RTS lead
is in the "off state." Even in loopback, the data will not flow unless RTS is asserted.