Comtech EF Data SMS-458B - Manual (Page 71)

SMS-458B Modem Protection Switch Revision 2
Theory of Operation MN/SMS458B.IOM
4–11
The active demodulators online status is indicated at J5 by form-C relay contacts. When
the prime is online or power is off, the relay is de-energized (COM to NC). When a
backup demodulator is online for that prime, the relay is energized (COM to NO).
4.1.7 Monitor and Control Theory of Operation
The Monitor and Control module uses an Intel 80C31 microcontroller operating at 5.5295
MHz. The microsystem supports 128K bytes of Read Only Memory (ROM) for code and
64K bytes of Random Access Memory (RAM) for data.
Of the 64K bytes, only 8K is used for RAM, the remaining 56K is used for memory-
mapped I/O.
Memory-mapped I/O includes:
• Real time clock/memory
• 8-channel analog-to-digital converter
• External buffered bus structure for overall switch control and status gathering
The 80C31 microcontroller supports a serial asynchronous communications channel
(EIA-232C) with a maximum baud rate of 9600 bit/s using the 5.5295 MHz reference.
A rechargeable battery maintains the system real time clock and switch configuration
through power-down situations.
Memory is maintained up to 30 days without power.
A full battery charge is attained after the modem is powered on for 48 hours.
4.2 Interface Switches
4.2.1 IDR/G.703 Interface Switch
4.2.1.1 General Description
The IDR/G.703 interface switch module switches all interface signals by relay. The prime
interface switch module (Figure 4-2) has two 50-pin female D connectors and four BNC
connectors. The terrestrial interface J1, J2, and J5 (top) is a DCE interface, and the prime
modem interface J3, J4, and J6 (bottom) is a DTE interface. The prime interface switch
module can plug into any of the even-numbered interface switch module slots (A2, A4,
A6, and A8) on the left side of the lower-rear panel.
The backup interface switch module (Figure 4-3) has one 50-pin female D connector and
two BNC connectors. The backup modem interface connectors J1 and J2 carry the G.703