QB50 System Requirements Document

TITLE: QB50 m-NLP Science Unit Interface Control DocumentDoc. No. MSSL-QB50-ID-12001-DRAFT aThe I2C I/F shall operate at 100 kHz clock speed.The I2C interface shall use a 7-bit address field.The I2C address of the Science Unit shall be fixed as TBC.The capacitance of the I2C bus shall be as specified in ND2.The only asynchronous signal from the SU to OBC is the RDY.All other SU communication is in response to explicit commands issued by the OBC.4.8.1 Science Unit I2C Command Packet StructureThe following packet structure shall be used to transmit commands from the OBC to theSU:CMD_ID:LEN:Param_n:one BYTE value for command identifierone BYTE value representing the number of 8-bit BYTES tofollow the LEN parameterparameters sent in BYTE format - LS BYTE is sent first ifparameter is a 16-bit WORDSee section 0 for details of commands.4.8.2 Science Unit I2C Reponses Packet StructureThe following packet structure shall be used to transmit responses from the SU to theOBC:RSP_ID:LEN:data_n:one BYTE value for command identifierone BYTE value representing the number of 16-bit WORDS tofollow the LEN parameterdata represented in 16-bit WORD format - LS BYTE is sent firstSee section 0 for details of commands/responses.Page 10 of 27