Registers are digital storage areas where information can be read or stored, or both.  There are 5 registers in your Tektronix scope, each register having 8 bits.   Three of the registers can be written to and read from the controller, two registers can only be read from the controller. Status Registers The two read-only registers are called status registers.  They contain the scope status information and make it available to the controller when asked.  Each of the 8 bits has a special meaning, so that the controller can tell what the status is.  For instance if the controller reads a value of 96 (i.e. binary %01100000) from a status register, it knows that bits 5 and 6 are set to 1 and all the others are still 0, so the controller can do some special task to fix those errors. Enable Registers The three read/write registers are the “filters” that limit the amount of information that the scope shows to the controller.  Each of the 8 bits can be “masked” to either pass information through, or to prevent it from passing.  A setting of 255 (binary %11111111) will enable all 8 bits and allow all the information to pass, but a setting of 1 (binary %00000001) will mask out all bits except bit 1.