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3 . 3
Display and Display Control
3 . 3 . 1
Overview
The Q2 has two screens, a drawing screen and a display screen, managed by means of rendering
coordinates. Display is performed for both these screens in accordance with double-buffering
control designated by the user.
When the GBM bit is set to 1 in the Q2's rendering mode register (REMR), a function can be used
that converts YUV or ∆YUV data color images to RGB data. When the GBM bit is cleared to 0,
the color palette can be used, enabling 256 colors to be specified out of a total of 260,000.
3 . 3 . 2
Double-Buffering Control
The Q2 uses double-buffering control to alternately switch the display and drawing areas located in
the UGM. An area switching operation is called a frame change. There are three modes for double-
buffering control: auto display change mode, auto rendering mode, and manual display change
mode. In auto display change mode, a frame change is performed each time the Q2 detects a frame
change timing. In auto rendering mode, a frame change is performed once only when the Q2 detects
a frame change timing after drawing is completed. In manual display change mode, the Q2
performs a frame change once only at the frame change timing following issuance by the SuperH
of a frame change directive to the Q2. These modes are specified by the double-buffering mode bits
(DBM) in the system control register.
Normally, when double-buffering control is performed, frame changes can be performed according
to the relevant mode by detection of a VSYNC synchronization pulse by the SuperH, followed by
setting of the rendering start bit (RS) to 1.
Frame change timing in double-buffering control is performed in frame units when the Q2 is
operated in non-interlace or interlace sync mode, and in field units when operated in interlace sync
& video mode.
When the Q2 is operated in interlace sync mode, the status register frame flag (FRM) is used for
VSYNC synchronization pulse detection by the SuperH. When the Q2 is operated in non-interlace
mode, synchronization pulses are detected using the vertical blanking flag (VBK). When the Q2 is
operating in interlace sync & video mode, since the first frame corresponds to the even field and the
second frame to the odd field, synchronization pulses are detected using VBK or FRM.
Examples are given below for Q2 non-interlace operation, with a description of the operation in
each mode.
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