MA28140 Datasheet, PDF (18/72 Pages) Dynex Semiconductor – Packet Telecommand Decoder

MA28140
- The TC Segment was transferred on MAP 63 (i.e., MAP
111111), which is dedicated to the transfer of Authentication
Control Commands. In this case, the Control Command
Processor is authorised to further process the TC Segment,
which will never be transferred to the Segmentation Layer.
In both cases, the contents of the indicated LAC Register is
incremented by one.
THE CONTROL COMMAND PROCESSOR
The function of the Control Command Processor is to
execute the special TC Segments called Authentication
Control Commands after being authorised by the Final
Authorisation Function. The formats of the various
Authentication Control Commands are specified in the section
on AU Control Commands next. Any TC Segment not
conforming to the specified formats (i.e., both in length and in
contents) are rejected and reported as not executable.
THE DELETION FUNCTION
The Deletion Function deletes the Authentication Tail of all
TC Segments authorised by the Final Authorisation Function.
The complete authentication process is meant to be
transparent to an observer placed at the receiving end of the
Segmentation Layer.
AU Control Commands
It is necessary to differentiate TC Segments containing the
Authentication Control Commands required to reconfigure the
AU. This is done by allocating the TC Segment Header
contents “all ones” to these particular segments, i.e.:
- Sequence Flags set to 11 (Unsegmented)
- MAP ID set to 111111 (MAP63)
TC Segments containing the Authentication Control
Commands shall always be authenticated. The formats of the
Authentication Control Commands are organised in three
groups as follows:
- One octet of TC Segment Header for all three groups.
- One octet following the Segment Header to specify the
Control Command Identifier
- Zero, four or eight octets of Control Command Data
Field, depending on the group.
Table 2 gives the complete list of Authentication Control
Commands, with Group numbers, Control Command IDs and
Command Names. Table 3 shows the format of the TC
Segment for each Group, complete with Authentication Tail.
Each Control Command is specified in the next subsections.
DUMMY CONTROL COMMAND
The purpose of this command is to serve as NOP (No
Operation) for testing purposes. After being authenticated, this
Control Command will have no effect. However, since the AU
has authenticated the Dummy Segment, the contents of the
LAC Register used during the authorisation process have
been incremented and a telemetry report prepared
accordingly.
SELECT KEY CONTROL COMMANDS
(a) Select Fixed Key
The AU selects the Fixed Key prior to authenticating the TC
Segment:
- If authentication is successful, the Fixed Key remains
selected.
- If authentication is unsuccessful, the key previously in
use remains selected.
(b) Select Programmable Key
The AU selects the Programmable Key for authentication
of the TC Segment:
- If authentication is successful, the Programmable Key
remains selected.
- If authentication is unsuccessful, the key previously in
use remains selected.
LOAD FIXED KEY IN PROGRAMMABLE KEY MEMORY
CONTROL COMMAND
This command reloads the Fixed Key set in the
Programmable Key memory with a single command
instruction. The key used for authenticating the TC Segment
containing the Control Command will be whatever key was
selected in the AU at the time the command was transmitted.
SET NEW LAC COUNT VALUE CONTROL COMMAND
The purpose of this Control Command is to set the value of
one of the three programmable LAC Counters: Principal,
Auxiliary or Recovery with LAC Identifiers 00, 01 and 10
respectively. If the LAC Identifier is set to 11, the command is
not executed and reported as not executable. As soon as the
TC Segment is authorised by the authentication process, the
specified LAC Count value is forced into the selected LAC
Register. Note that the 22 MSBs of the 30-bit Recovery LAC
Register are permanently set to all ones, therefore those same
bits in a Set New Recovery LAC Count Value Control
Command are ignored by the AU. The key used for
authenticating the TC Segment containing the Control
Command will be whatever key was selected in the AU at the
time the command was transmitted.
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