CANOGA PERKINS 2340 Universal Fiber Optic Modem - Manual (Page 23)

EdgeAccess® Universal Chassis System
Model 2340 Model User Manual 3-9
• External mode: Use when the DTE provides the clock or when the 2340 is used as a tail circuit
connecting to a DCE. The other device sends this clock to the modem as the TD Timing signal.
Go to the Functional Configuration screen and set the interface configuration values: select
External mode, then set the TD Timing source to SCTE or SCTE Sampled for a gapped clock.
See Figure 5.
RX Data
RX Clock
Internal
Clock
TX Clock
TX Data
RXD
SCR
SCT
SCTE
TXD
INTERFACE MODEM MAIN BOARD
External Mode With SCT Ignored
SCTE Used for TD Timing
SCR Used for RD Timing
RX Data
RX Clock
Internal
Clock
TX Clock
TX Data
RXD
SCR
SCT
SCTE
TXD
INTERFACE MODEM MAIN BOARD
External Mode With SCT Input
SCTE Used for TD Timing
SCT Used for RD Timing
Figure 5. External Operating Mode
• Internal mode: Use when this 2340 generates the clock and sends it to the DTE on the SCT
signal. Go to the Functional Configuration screen and set the interface configuration values: set
the interface type, then select Internal mode, then set the Internal data Rate; then set the TD
Timing source to SCT for most applications or to SCTE or SCT Inverted for high data rates or a
long cable to the DTE. See Figure 6.
PLD
RX Data
RX Clock
Internal
Clock
TX Clock
TX Data
RXD
SCR
SCT
SCTE
TXD
Internal Mode Without Turnaround Clock
SCT Used for TD Timing
SCR Used for RD Timing
INTERFACE MODEM MAIN BOARD
RX Data
RX Clock
Internal
Clock
TX Clock
TX Data
RXD
SCR
SCT
SCTE
TXD
INTERFACE MODEM MAIN BOARD
Internal Mode With Turnaround Clock
SCTE Used for TD Timing; the DTE loops the clock from SCT toward SCTE
SCR Used for RD Timing
Figure 6. Internal Operating Mode