Comtech EF Data SDM-650B - Manual (Page 58)

Configuration SDM-650B Satellite Modem
3–16 Rev. 5
Data received by the modem is output on the RD lines, while the recovered clock is
output on the Serial Clock Receive (SCR) lines. For applications that require the rising
edge of the clock to occur in the middle of the data bit time, Receive Clock Normal mode
should be selected.
Invert mode puts the falling edge of SCR in the middle of the data bit. This selection can
be made from the front panel in the Configuration menu.
The RTS lines are jumpered to the CTS lines, since the modem does not support polled
operation. Data Set Ready (DSR) indicates that the modem is powered up. Receive Line
Signal Detect (RLSD) indicates that an RF carrier is being received and demodulated
with a sufficiently low error rate for the decoder to remain locked.
The V.35 interface also provides bi-directional relay loopback of both the clock and data
at the DCE interface.
In loopback from the DTE side, SD is connected to RD, and either SCT or SCTE (in
Internal or External mode) is looped back to SCR.
In loopback from the modem side, the received data and recovered clock are routed back
to the modulator input for re-transmission.
Loop timing is supported by the selection of jumper JP10 on the front edge of the card.
When in the ON position, the internal clock (SCT) is replaced by the clock recovered
from the receive (IF) data (RD). Active loop timing is indicated by a yellow light on the
front edge of the card.
The JP10 REM setting is used when loop timing is supported by software on the M&C,
and will be included in the front panel menu.
Three fault outputs are provided on dry contact FORM C relays:
• Common Equipment
• Modulator
• Demodulator
The faults are available on the Fault connector on the modem rear panel. Generation of
these fault conditions is described in Chapter 4. Fault indicators are also provided on TTL
open collector drivers on the V.35 connector.
• The TTL MOD fault indicates a Modulator fault or Common Equipment fault.
• The TTL DEMOD fault indicates a Demodulator or Common Equipment fault.