AL300 datasheet(21/64 Pages) ETC

21 / 64 page

AL300

November 28, 2001

6.9.3 Bypass Mode

This mode is only good for the application in which the input and output resolution are the same.

Basically, the input clock and H-sync timing are used for the output timing and therefore the picture is

not zoomed. However, the data can be processed by all of the internal data processing hardware and

OSD circuit, except for the scaling function. Only some registers that are used for the previous two

modes are affected. Details about programming the related registers can be found in the Register

Definition section.

6.10 Interrupt

The interrupt signal can be triggered by one or a combination of any of the three following events.

1. When the line rate of the input video changes.

2. When input VSYNC arrives.

3. When the odd field arrives.

interrupt. The first interrupt source is helpful in automatically detecting the mode changes. The

second interrupt source can be used to do a periodic routine during the vertical blanking region. The

last interrupt source can be used to do a periodic routine in the odd field of interlaced input video.

Upon receiving the interrupt request from the AL300, the micro-controller needs to first check the

interrupt event by reading the register IREQSTATUS (Reg. #65h) to decide what operations to

perform. After the interrupt routine is complete, the interrupt status register is reset by writing the

6.11 On Screen Display (OSD)

Two independent On-Screen-Display (OSD) windows provide overlay for a control menu, text, or

caption on the output display. The AL300’s OSD is very flexible in the way that the font, size, and

display location are all programmable. The internal 1K byte SRAM provides storage for the OSD

information. The OSD can be operated with only this internal SRAM or with an external ROM to

store font tables or even larger bitmaps.

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