A sensor controller for use in a position detector for detecting a position of a position indicator on a touch surface, comprising a controller and a transmitter coupled to the controller, wherein the controller is configured to output a value of a primary symbol to be sent to the position indicator, wherein the controller is configured to output a value of a secondary symbol to be sent to the position indicator, wherein the transmitter is configured to generate a primary transmission signal including a primary first chip string produced by cyclically shifting a spread code having autocorrelation characteristics by a primary shift quantity based on the value of the primary symbol to be sent, and to send the generated primary transmission signal to the position indicator via the touch surface, wherein the transmitter is configured to generate a secondary transmission signal including a secondary first chip string produced by cyclically shifting the spread code by a secondary shift quantity based on the value of the secondary symbol to be sent, and to send the generated secondary transmission signal to the position indicator via the touch surface, wherein the primary symbol takes multiple values, wherein the primary symbol takes any one of a total number of values wherein the total number is indicated by a power of 2, the primary symbol being represented by a bit string having a predetermined bit length, wherein the secondary symbol takes any one of 1 or more values respectively different from any one of the total number of values wherein the total number is indicated by the power of 2, and wherein: - the total number of values taken by the primary symbol form commands, each indicating a content of an instruction for the position indicator, and - the 1 or more values taken by the secondary symbol forms a preamble indicating a start of the command. wherein the controller is configured to output a value of a primary symbol to be sent to the position indicator, wherein the controller is configured to output a value of a secondary symbol to be sent to the position indicator, wherein the transmitter is configured to generate a primary transmission signal including a primary first chip string produced by cyclically shifting a spread code having autocorrelation characteristics by a primary shift quantity based on the value of the primary symbol to be sent, and to send the generated primary transmission signal to the position indicator via the touch surface, wherein the transmitter is configured to generate a secondary transmission signal including a secondary first chip string produced by cyclically shifting the spread code by a secondary shift quantity based on the value of the secondary symbol to be sent, and to send the generated secondary transmission signal to the position indicator via the touch surface, wherein the primary symbol takes multiple values, wherein the primary symbol takes any one of a total number of values wherein the total number is indicated by a power of 2, the primary symbol being represented by a bit string having a predetermined bit length, wherein the secondary symbol takes any one of 1 or more values respectively different from any one of the total number of values wherein the total number is indicated by the power of 2, and wherein: - the total number of values taken by the primary symbol form commands, each indicating a content of an instruction for the position indicator, and - the 1 or more values taken by the secondary symbol forms a preamble indicating a start of the command. - the total number of values taken by the primary symbol form commands, each indicating a content of an instruction for the position indicator, and - the 1 or more values taken by the secondary symbol forms a preamble indicating a start of the command.