4.Send, Receive
Data is sent to and received from the scanner. With this command, the transfer length and assigned length must be the same as the actual number of data bytes. For example, when the ESC G (Start reading) command is to be sent to the scanner, the transfer length must be 2 bytes; otherwise, an error occurs and the command is not executed. If the assigned length is 0, the command is ended.
Unit Attention Condition
When the power is turned on, or a reset is performed with the RESET condition or Bus Device Reset message, the scanner enters the Unit Attention condition. The Unit Attention condition then continues until a command other than Request Sense or Inquiry is received from the Initiator.
If a command other than Request Sense or Inquiry is received from an Initiator with a pending Unit Attention condition, the scanner sends the Check Condition status without executing the command. If the Request Sense command is received while in the Unit Attention condition, the scanner sends the Unit Attention sense data and clears the Unit Attention condition.