An EFM/EFM+ encoder and a method thereof, performing digital sum value (DSV) protection in an Eight-to-Fourteen/Eight-to-Fourteen Plus (EFM/EFM+) encoding system to generate a data frame to be recorded on a recording medium. The method comprises modulating source data to the data frame having a predetermined number of channel bits, determining merging bits and DSV based on the channel bits, and changing the predetermined number of the channel bits in the data frame based on the DSV and the merging bits. The changing the predetermined number of the channel bits comprises inserting or removing a channel bit at the end of the data frame.