The 8 bit frame sequence number field supports a

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Unformatted text preview: ithin this layer. The FRAME SEQUENCE NUMBER enables the FARM to check the sequentiality of incoming Type-A TC Frames. The 8-bit FRAME SEQUENCE NUMBER field supports a modulo-256 sequence count. The FRAME SEQUENCE NUMBER is Virtual Channel dependent; i.e., the Transfer layer shall maintain a separate FRAME SEQUENCE NUMBER for each of the (up to 64) VIRTUAL CHANNELS. Note that the COP does not use this field when operating with Type-B TC Frames; in this case the contents of the FRAME SEQUENCE NUMBER field shall be set to “all zeros”. 4.2.1.2 Transfer Frame Data Field. The FRAME DATA FIELD, which is of variable length up to a maximum of 1019 octets (1017 octets if the FRAME ERROR CONTROL FIELD is present), shall contain either an integral number of octets of telecommand data corresponding to one TC Frame Data Unit or an integral number of octets of Control Command information. The FRAME DATA FIELD shall be inserted directly after the Frame Header with no filler between. 4.2.1.2.1 TC Frame Data Unit. The TC Frame Data Unit is supplied by the Segmentation layer. The content of a TC Frame Data Unit is defined in Section 3.3.1. 4.2.1.2.2 Control Commands. There are two Control Commands defined: UNLOCK and SET V(R). The action to be taken when the FARM receives one of the Control Commands is defined in Reference [7]. All other bit combinations for Control Commands are reserved by the CCSDS for future application. UNLOCK: The UNLOCK Control Command consists of a single octet containing “all zeroes”. SET V(R): The SET V(R) Control Command consists of three octets with the following values: 10000010 00000000 XXXXXXXX where XXXXXXXX is the value to which the FARM should set V(R), the Receiver_Frame_Sequence_Number. This octet should therefore be set to the Sequence Number which will be put into the Header of the next Type-A TC Frame to be transmitted on that Virtual Channel. CCSDS 202.0-B-2 Page 4-7 CCSDS HISTORICAL DOCUMENT November 1992 CCSDS HISTORICAL DOCUMENT CCSDS RECOMMENDATION FOR TELECOMMAND: DATA ROUTING SERVICE 4.2.1.3 Transfer Frame Error Control Field. The purpose of this opt...
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This document was uploaded on 03/06/2014.

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