Release 1
DAMS-NT DigiRIT Operation Manual
12/14/2012
Microcom Design, Inc.
10
While the DAMS-NT specification allows the StartPattern to be configured, this is not possible
in the DigRIT since the Configuration Interface is not implemented. As such, the start pattern
has been hard coded based on the de facto standard. While the DAMS-NT specification allows
for any four binary byte values, most DAMS-NT sites are configured to use the hexadecimal
pattern 0x534D0D0A that correlates to the ASCII characters “SM” (i.e. Start Message) followed
by a CR/LF. In addition to being compliant, use of this pattern in the DigiRIT also means the
entire header is ASCII.
Table 1: 55-Character DCP Message Header Format
Ofs
Name
Len
Format
Description
0
StartPattern
4
String
“SM”+CR+LF (0x534D0D0A)
4
SlotNum
3
Digits-Zero Filled
LRIT Virtual Channels
7
Channel
3
Digits-Zero Filled
DCS Spectrum Channel Number
10
Spacecraft
1
Character
‘E’ or ‘W’
11
Baud
4
Digits-Zero Filled
See Below
15
StartTime
11
YYDDDHHMMSS
UTC Time of message start (i.e. frame
synch)
26
SignalStrength
2
Digits-Zero Filled
Signal strength in dB
28
FreqOffset
2
+/- 1 Digit
Sign character followed by 1 digit. In
units of 50Hz
30
ModulationIndex
1
‘N’, ‘H’, or ‘L’
N=normal, H=high, L=low
31
DataQuality
1
‘N’, ‘F’, or ‘P’
N=normal, F=fair, P=poor
32
ErrorFlags
2
Hex Characters
2 Hex characters representing up to 8 bit-
error or message flags. See Table 2.
34
OrigAddress
8
Hex Characters
DCP Address – See Below
42
DcpAddress
8
Hex Characters
DCP Address – See Below
50
Length
5
Digits-Zero Filled
Number of message bytes to follow
The slot number field, in the DAMS-NT specification corresponded to “demodulator slots” that
could be tuned to any DCS channel. In the DigiRIT, this value can be configured to supply one
of three types of values (see Section 3.2.2.3). The default setting is to fill this filed with the
LRIT Virtual Channel (VC) the message was received on. The LRIT specification provides for
64 virtual channels to be used by different products, and within a product group by different
priorities. Currently, DCS messages utilize three of these Virtual Channels based on a priority
scheme. As such, this zero-filled, numeric field typically correlates the LRIT VC to the “slot
number”. The other two user configurable options for this field are a received sequence count
number or a DRGS source code identifier; see Section 3.2.2.3 for more information on these two
options.
The Channel is the numerical value of the DCS channel the message was received on. This
information is provided in the LRIT stream and is simply copied verbatim.
The Spacecraft field designates the GOES satellite the message was received on, East or West.
Note this is the spacecraft the original DCS message was transmitted through, not the LRIT
spacecraft. As with the Channel field, the information is provided via the LRIT data and is
simply copied.