A printing apparatus receives, as serial data, a plurality of commands for driving a printhead including arrayed print elements to perform printing. Then, a first signal is internally generated in the apparatus, and a second signal is generated based on the position of a conveyed print medium. In addition, each command is extracted from the received serial data. While switching over the first and second signals based on each command, the printhead is driven to perform a preparation operation prior to image printing by the printhead based on the first signal and to print an image based on image data on the print medium based on the second signal. Upon switchover of the first signal to the second signal, switchover to the second signal is controlled after disabling the first signal for a predetermined period.