WT8043

Weltrend

Semiconductor,

Inc.

2F., No. 24, Industry E. 9th Rd.

Science-Based Industrial Park

Hsin-Chu, Taiwan, R.O.C.

Tel:

886-35-780241

Fax: 886-35-770419

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Appication Description

General Description

Figure 1-1 and 1-2 is a simplified functional block diagram of the WT8043. It

includes the following functional blocks: sync pulse polarity detector; horizontal

and vertical frequency discriminator, mode selector.

The Sync pulse polarity detector accepts separete H and V sync signals with any

polarities. It determines their polarities and sends the polarity information to the

mode selector for video mode selection. It alos generates -H and -V signals in spite

of their input polarities.

The H and V frequency discriminator determines the frequency range of H and V

sync signals. The mode selector determines which operating video mode it should

be, according to the frequency range and polarity of H and V sync signals. The

operating video modes include the standard IBM VGA (640x350, 640x400,

640x480), super VGA (800x600) and IBM8514/A (Inerlaced, Non-interlaced),

VESA VGA & SVGA mode, VESA new SVGA mode, XGA (1024x768), and

1280x1024 mode, also including NEC 24kHz and 3 VESA New 75Hz timing

modes.

The mode selector also generates output signals that represent the frequency range

of H. sync signal. The H sync signal is divided into 6 frequency ranges (3 ranges

for WT8043N20) according to Fig. 2, WT8043 has preset the discriminating points

between frequency ranges.

However, it also offers the flexibility for providing

user-defined discriminating points for non-standard video modes.

The digital noise filter is used for rejecting noise on the incoming horizontal and

vertical synchronous signals. The input section uses two techniques to improve

noise rejec-tion. So the low level noise and the large short duration noise spikes

will be rejected. Horizontal synchronous pulse width under 0.56

µs and vertical

synchronous pulse width under 0.56

µs will be considered as noise.