Comtech EF Data SMS-458B - Manual (Page 80)

SMS-458B Modem Protection Switch Revision 2
Theory of Operation MN/SMS458B.IOM
4–20
4.5 Data Switch Controller Card
The data switch controller (Figure 4-8) resides in the data switch (lower) section in the
switch. The card performs two main functions:
• The card decodes M&C commands in order to control the data switching matrix.
• The card contains a synthesized data source, which is used to keep a data stream
to the offline modulator. This is done so the offline modulator does not show a
faulted condition due to loss of data.
Since the data that is fed to the offline modulator as an all 1s pattern, the modem will
show AIS indication. The data rate is programmed automatically when the user programs
the switch. The on-board oscillator has a fine tune adjustment, R29 (which is set at the
factory), for the oscillator frequency, and can be monitored by connecting a frequency
counter to J3.
The data rate of the oscillator frequency can be programmed from 32 to 45 Mbit/s.
DATA BUS
CARD SEL
FROM M&C
X 8 M&C
INTF
L
A
T
C
H
COMMAND
X 22
BASEBALL
DRIVERS
TO BASEBALL
SWITCH 1
TO BASEBALL
SWITCH 22
X 22
TO IF SWITCH +12V
DECODE
SYNTH LEVEL
FORMATER
ALL ONES
DATA
CRYSTAL
OSCILLATOR
R29
Figure 4-8. Data Switch Controller Card