NEC uPD72257, Preliminary User'S Manual

Page: 156 / 343

The values VInSYNCDECODE.14SCN[9:0] and VInSYNCDECODE.34SCN[9:0]
are described in pixel clocks. By use of these signals a internal "middle of
scanline" signal is generated and HSYNC, VSYNC and the field information are
derived.
Caution
Even if separate horizontal and vertical synchronization signals are supplied
externally (VInCONTROL.SYNCSEL[1:0] = 10
B
), the synchronization separator
timing in VInSYNCDECODE has to be set correctly.
VInSYNC polarity The polarity of the external synchronization signal is selectable by
VInCONTROL.SYNCINV:
• VInCONTROL.SYNCINV = 0: VInSYNC1/VInSYNC2 is not inverted,
i.e. high level denotes active synchronization
• VInCONTROL.SYNCINV = 1: VInSYNC1/VInSYNC2 is inverted, i.e.
low level denotes active synchronization
Synchronization
information
The detection of synchronization information can be monitored in
VInSTATUS.HSYNC, VInSTATUS.VSYNC and VInSTATUS.FIELD.
6.2.3 Synchronization status information
The status of the internal synchronization signals, derived from the external Video
Input, are monitored by some status bits in the Video Input status register:
• VInSTATUS.FIELD indicates the current field information
• VInSTATUS.VSYNC indicates the current status of the internal
VSYNC signal
• VInSTATUS.HSYNC indicates the current status of the internal
HSYNC signal
6.3 Video Capturing
6.3.1 Video capturing modes
The Video Input module can capture interlaced as well as progressive scanned
video data frames.
It distinguishes automatically between both modes by evaluating the field
information, acquired from the timing reference bytes in case of ITU-R656 data
input respectively from the composite or separate synchronization signal
VInSYNC1/VInSYNC2.
Depending on the recognized mode the video data is stored in two framebuffers
in case of an interlaced video respectively in a single one in case of a progressive
scanned video.
Progressive video In case a progressive scanned video is detected, all video data is stored in the
framebuffer, starting at address VInSTARTADDR2.
The scanline monitor register VInACTSCANLINE indicates always second field by
VInACTSCANLINE.AFLD = 1 and the scanline counter
VInACTSCANLINE.ACTSL[11:0] counts linearly from 0 to maximum line number.
Chapter 6 Video Input (Ravin-M only)
156
Preliminary User's Manual S19203EE1V3UM00