WT8043
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.
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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ETC [ ETC ]
