Comtech EF Data SMS-458B - Manual (Page 78)

SMS-458B Modem Protection Switch Revision 2
Theory of Operation MN/SMS458B.IOM
4–18
4.3.3 Address Decoder/Driver Theory of Operation
The address decoder/driver interfaces the:
• M&C data bus
• Address
bus
• Control
lines
• Serial
interface
Addresses of the peripheral devices, both on and off of this card, are latched and decoded
to select each device. The data bus is bidirectionally buffered to and from the M&C card.
The data bus and decoded address lines are buffered off this card as they are output to the
other modules.
The address decoder/driver formats the serial data communication to and from the M&C.
All interface drivers and receivers for external communication are on this module.
The fault lines from the interface switch modules are routed to this card. The M&C reads
the faults at regular intervals to update its own registers.
The address decoder/driver card contains the following fault relays:
• M:N
summary
• Demodulator
signal
• Controller
The M&C control the M:N summary and demodulator signal fault relays directly.
A “watchdog” timer controls the controller fault. The M&C must reset the “watchdog”
timer at regular intervals, or the controller fault will set.