JAJSMU1 February 2023 DS90UB638-Q1
PRODUCTION DATA
In Internal FrameSync mode, an internally generated FrameSync signal is sent to the attached FPD-Link III Serializer through a GPIO signal in the back channel.
FrameSync operation is controlled by the FS_CTL 0x18, FS_HIGH_TIME_x, and FS_LOW_TIME_x 0x19–0x1A registers. The resolution of the FrameSync generator clock (FS_CLK_PD) is derived from the back channel frame period (see BC_FREQ_SELECT[2:0] in Table 7-86). For example, each 50-Mbps back channel operation, the frame period is 600 ns (30 bits × 20 ns/bit), and for 2.5-Mbps back channel operation, the frame period is 12 μs (30 bits × 400 ns/bit).
Once enabled, the FrameSync signal is sent continuously based on the programmed conditions.
Enabling the internal FrameSync mode is done by setting the FS_GEN_ENABLE control in the FS_CTL register to a value of 1. The FS_MODE field controls the clock source used for the FrameSync generation. The FS_GEN_MODE field configures whether the duty cycle of the FrameSync is 50/50 or whether the high and low periods are controlled separately. The FrameSync high and low periods are controlled by the FS_HIGH_TIME and FS_LOW_TIME registers.
The accuracy of the internally generated FrameSync is directly dependent on the accuracy of the 25-MHz oscillator used as the reference clock and timing values should be scaled if reference other than 25 MHz is used.
The following example shows generation of a FrameSync signal at 60 pulses per second. Mode settings:
Based on mode settings, the FrameSync is generated based upon FS_CLK_PD of 600 ns.
The total period of the FrameSync is (1 / 60 hz) / 600 ns or approximately 27778 counts. The high time is programmed to 2778 and the low time is programmed to 25000.
For a 10% duty cycle, set the high time to 2777 (0x0AD9) cycles, and the low time to 24999 (0x61A7) cycles: