Comtech EF Data SDM-650B Installation And Operation Manual page 299

SDM-650B Satellite Modem
The MIL-STD-188-114 interface provides a Send Timing (ST) clock signal at the modem
transmit data rate. In the INTERNAL clock mode, the data to be transmitted, Send Data
(SD), must be synchronized to ST. In the EXTERNAL clock mode, clock is accepted on
the Terminal Timing input (TT) to clock in the data to be transmitted. In either case, the
phase relationship between the clock and data is not important, so long as it meets the
jitter specifications of MIL-STD-188-100, because a clock phase correction circuit is
provided, which shifts the clock away from the data transition times. If EXTERNAL
clock mode is used, the clock must be long-term synchronous with the synthesizer
reference, unless it is selected to "Transmit" clock.
Data received by the modem is output on the Receive Data (RD) lines, while the
recovered clock is output on the Receive Timing (RT) 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 RT in the
middle of the data bit.
The Request to Send (RS) lines are hard-wired to the Clear to Send (CS) lines, since the
modem does not support polled operation.
Data Mode (DM) indicates that the modem is powered up.
Rev. 5
Receive N
Data Rate
(kbit/s)
56 7
64 8
128 16
256 32
512 64
1024 128
1544 193
2048 256
Receive K
Data Rate
(kbit/s)
56 64
64 64
128 32
256 16
512 8
1024 4
1544 2
2048 2
K L Receive
VCO
Frequency
(kHz)
64 7 3584
64 8 4096
32 16 4096
16 32 4096
8 64 4096
4 128 4096
2 193 3088
2 256 4096
L Receive
VCO
Frequency
(kHz)
7 3584
8 4096
16 4096
32 4096
64 4096
128 4096
193 3088
256 4096
Trojan Interface
G–3