QB50 System Requirements Document

5.4 Command Packet Structure to Science UnitThe following packet structure shall be used to transmit commands from the OBC to theSU:where:CMD_ID, LEN, param_0, param_1…param_LEN-1CMD_ID:LEN:8-bit value for command identifier8-bit value representing the number of BYTES tofollow the LEN parameterParam_n: parameters sent in BYTE format - LS BYTE is sent first for16-bit WORD parameters.See section 5.9 for details of commands/responses..5.5 Reponses Packet Structure to CubeSatResponse packets are of a FIXED size. The following packet structure shall be used totransmit responses from the SU to the OBC:Where:RSP_ID, SEQ_CNT, 518 DATA BYTESRSP_ID:8-bit value is a copy of the CMD_ID field from the originatingcommand.SEQ_CNT: 8-bit value representing a sequential count of packets. The countervalue shall roll-over to X”00” having reached maximum count(X”FF”).DATA:This is of a fixed packet size: 518 BYTES. 16-bit WORDs shall besent LS BYTE is sent firstTotal Response packet length is therefore 520 BYTES.See section 5.9 for details of commands/responses.