Aspects of the subject technology relate to electronic devices with displays. A display may include display control circuitry including an internal oscillator and one or more counters. The counters may be used to calibrate a display line time to a system line time to ensure that each displayed frame is synchronized with received display data frames from system circuitry for the electronic device. The counters may include a first counter that maintains a current-row count during operation of a current row of display pixels during a current display frame and a second counter that maintains a current-frame count that indicates a number of counts accumulated during the current display frame. The current-row count and the current-frame count may be referenced to the system line time during operation of each pixel row to remove any errors accumulated during operation of the previous pixel rows.