0 b 2 page 4 2 ccsds historical document november

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Unformatted text preview: ation of the Transfer Layer CCSDS 202.0-B-2 Page 4-2 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE 4.2.1 TC TRANSFER FRAME FORMAT The TC Frame (Figure 4-2) contains the following major fields: Major Field Length (Octets) FRAME HEADER FRAME DATA FIELD FRAME ERROR CONTROL (Optional) 5 Variable (up to 1019) (2) 1024 octets (maximum) The maximum TC Frame length allowed by a particular spacecraft or ground implementation on a particular Virtual Channel may be less than the maximum specified here. FRAME HEADER (5 octets) 2 octets 2 octets VERSION BYPASS CONTROL NUMBER FLAG COMMAND FLAG 2 1 S SPACE VIRTUAL P CRAFT CHANNEL ID ID A R E 2 1 10 6 1 octet FRAME LENGTH FRAME FRAME SEQUENCE DATA NUMBER FIELD 10 FRAME ERROR CONTROL (opt) 8 (16) 1019 octets (max) Figure 4-2: TC Transfer Frame Format 4.2.1.1 Transfer Frame Header. The FRAME HEADER of the TC Transfer Frame consists of the following fields, grouped into octets as shown: Field Version Number Bypass Flag Control Command Flag Reserved Spares Spacecraft ID #Bits 2 1 1 2 10 Virtual Channel ID Frame Length 6 10 Frame Sequence Number CCSDS 202.0-B-2 #Octets 8 Page 4-3 CCSDS HISTORICAL DOCUMENT 2 2 1 5 octets November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE The first two octets of the FRAME HEADER contain the following field allocations: (1) VERSION NUMBER (Bits 0,1) The VERSION NUMBER occupies the two most significant bits of the Frame Header. Future changes in the TC Transfer Frame structure may be accommodated by changing the VERSION NUMBER. At present, only Version “1” of the TC Transfer Frame (the format specified herein) is defined. It shall be identified by setting Bits 0,1 to value “00”. (2) BYPASS FLAG (Bit 2) The single-bit BYPASS FLAG controls the application of “Frame Acceptance Checks” by the receiving spacecraft. ALL Frames received by the spacecraft first undergo a basic standard set of “Frame Validation Checks”, which are applied regardless of the setting of...
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