DIRECTV R15 Installation Guide - Page 14

DIRECTV Set-Top Box Information for the Installer Start Send STB Response Send STB Response Send STB Response A = ACK_RESET = DATA_ERROR = CMDBUF_OVFL Reset Command Parser (Parser is free) *Command Prefix (0xFA)? NO Send STB Response = NACK_PREFIX YES **Command Parser attaches to current data port (Parser is in use) *Known Command? NO Send STB Response = NACK_CMD YES NO *2 Byte Command? YES Read 2nd Byte of a 2 Byte Command Input NO Parameters? YES Send STB Response = NACK_PARAMS NO *Correct # of Input Parameters? YES Send STB Response = ACK_PARAMS Execute Command and send Return Data Stream as appropriate (Parser is Busy) Send STB Response = NACK_FCNOK NO Command completed successfully ? YES Send STB Response = ACK_FCNOK (Parser is not busy) *Known NO Command? YES Send STB Response = ACK_CMD A Figure 4-1. Service Command Parser Flowchart DIRECTV, Inc. Version 2.2 Page 14 of 42 March 5, 2008 DTV-MD-0058