Comtech EF Data SMS-758 - Manual (Page 80)

Theory of Operation SMS-758 Modem Protection Switch
4–20 MN/SMS758 Rev. 3
4.6.3 V.35/RS-232 Interface Switch
The V.35/RS-232 interface switch module switches all interface signals by relay.
Interface types can be changed between V.35 and RS-232 by the SPDT toggle switch
located on the back of the daughter card. Both the prime and backup interfaces must be
in V.35 mode or RS-232 mode in order to operate correctly.
The prime interface switch module (Figure 4-6) has two 25-pin D connectors:
•
J1 (top) for terminal equipment is a DCE interface.
•
J2 (bottom) for the prime modem is a DTE interface.
The backup interface switch module (Figure 4-7) has one 25-pin D connector. The
backup modem (J1) is a DTE interface.
The prime interface switch module can plug into any of the interface switch module slots
(A1 through A8) on the left side of the lower rear panel. The backup interface can plug
into either A9 or A10.
When the prime interface switch module (or the M:N switch itself) is powered down or
in the default position, all signals are routed between the terminal equipment and the
prime modem.
Modulator and/or demodulator signals can be independently switched to either of the two
backup modem interface switch modules, if the independent mod/demod firmware is
used. If modem switch firmware is used, then both the modulator and demodulator
switch to the backup when either the prime modulator or demodulator indicates a fault.
A buffered set of transmit clock (SCTE) and master clock (MC) signals is switched to
the “hot standby” backup modulator or demodulator, or the offline prime modulator and
demodulator when a backup operation occurs.
The fault lines from the modem connector are routed through the interface switch
modules to the M&C.