SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Discrete Sync signal handling varies among different sending devices. The information that must be conveyed includes the pixel data value, field ID, horizontal blanking, and vertical blanking. Many devices can be configured to adjust the timing of the signals relative to each other.
In this section, DATA will be depicted as 8 bits. However, discrete sync does optionally support 16-bit and 24-bit data input. Type 1 is named after a generic five pin interface between the sending and receiving devices.
In Figure 9-27, P0 represents the first pixel in the horizontal blanking interval following the last vertical blanking line of the previous field or frame. HSYNC specifies the horizontal blanking region and VSYNC specifies that the P0 pixel is in the vertical sync area. HSYNC can be a strobe that is active one or more cycles and can deassert before the actual end of horizontal blanking or HSYNC may be active for the full duration of horizontal blanking.
Likewise, VSYNC can be a strobe that is active one or more cycles and can deassert before the actual end of vertical blanking or VSYNC may be active for the full duration of vertical blanking.
FID can change at this pixel or it may change later. For interlaced source, though, the FID will be inverted for this pixel at the same time point in the next field. So, it does not really matter when FID is captured. Many sending devices allow the location of FID changes to be programmable.
In this diagram and all others in this document, the active polarities of the interface signals can be either high or low. For the sake of uniformity in this document, all polarities are drawn active high. Also, different vendors have different datasheet names for the interface signals.
Figure 9-28 shows the P0 pixel being the first Chroma Channel data value in the Vertical Ancillary Data region. HSYNC is definitely de-asserted by now since P0 is no longer in horizontal blanking. ACTVID may or may not be active for Vertical Ancillary Data. Some devices consider these pixels to be Active (as in non-horizontal blanking). Other devices consider only video to be ACTIVE Video.
Following the vertical blanking region, the video portion of the field or frame starts. Figure 9-29 shows the horizontal blanking area in this video portion of the field or frame. P0 is the first pixel in the horizontal blanking. HSYNC is active for one or more pixel clocks. VSYNC is inactive in this video area. FID can change here. ACTVID is low since P0 is horizontal blanking.
In Figure 9-30, P0 represents the first Chroma pixel in the Active video line. HSYNC is inactive, since P0 is in the active video region. Likewise, VSYNC is inactive. FID may or may not change here. ACTVID is high to signal capturing of video pixels.