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

13

H/V Frequency Divisions and Video Modes

Figure 2 illustrates the typical frequency ranges of H and V sync signals for

display monitors. The operating video modes are determined by the H and V

frequencies, and occasionally, by their polarities. The typical video modes of

display monitors include the NEC 24k mode, IBM VGA, VESA VGA, European

VGA/Super VGA, Apple MAC II, VESA Super VGA, IBM 8514/A,3 VESA New

75Hz modes, XGA, and 1280x 1024.

WT8043 can determine 18 standard video modes (as shown in Table 1) according

to H and V frequencies and polari-ties. These standard video modes include the

IBM VGA, VESA VGA, VESA super VGA and IBM 8514/A. This provides the

users with the capability to adjust the screen size for different modes.

WT8043 pre-sets the discriminating points both on H and V frequencies. The

discriminating points for H sync are 33KHz, 36.2KHz, 45KHz, 52KHz, 62KHz

and 72KHz. These discriminating points will be able to identify various video

modes as shown in Fig. 2. WT8043 also provides the flexibility for users to define

these discriminating points through mask option.

The tolerance for H sync frequency discrimination is 0.05KHz. For instance, the

33KHz discriminating point will be able to distinguish the H sync frequency that is

either "less than or euqal to" 32.95KHz, or "greater than or equal to" 33.05KHz.

There is an ambiguous region between 32.95KHz and 33.05KHz.

WT8043 has three discriminating points, 64Hz, 73.5Hz and 78Hz, for the V sync

signal as shown in Fig.2. The tolerance is 0.01Hz. The discrimination results of V

sync frequency are used internally for mode selection.

Base on the package consideration, IBM VGA mode and VESA VGA mode (both

have same resolution: 640x480, 640x400, 640x350) are decoded on same open

Drain structure output pins (e.g. pin 14 to pin 16 for N20P1 pin type package). In

case of these whole 6 modes decoding is needed, the horizontal frequency

discrimination pin F33k or F36k must take into consideration.

The horizontal

frequency of IBM VGA mode is 31.4kHz, and VESA IBM VGA mode is 37.5kHz.

Using F33k or F36k pin can clearly identify these two standard modes. The

decoding circuit is attached on application section for reference.