Z90251 Datasheet, PDF (50/97 Pages) Zilog, Inc. – eZVision 200 Television Controllers with OSD

Z90255 ROM and Z90251 OTP
32 KB Television Controller with OSD
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Bit 5, Fringe Enable, sets the fringe effect ON or OFF.
Bit 4, Smoothing Effect Enable, sets smoothing ON or OFF, and is available for
2X and double width characters.
Bit 3, RGB Polarity, sets color polarity of OSD color output signals to positive or
negative.
Bits 2, 1, and 0 form the color for the master background. The eight possible
colors are the same ones listed in Table 21.
Video Refresh RAM Access
The Z90255 supports 12-bit character data. Nine bits, P8 and P7 through P0,
contain character code. Three additional bits, C2 through C0, contain color palette
information. See Figures 15.
Color Palette Selection bits serve as a 3-bit Color Index to the color palette look-
up table. When software writes Character Byte data (7-0) into VRAM, it also
takes the data in the color index register and writes the corresponding Color
Palette Selection Bits (10-8) and the most significant bit of character data (P8).
When updating 3-bit color index data, the most significant bit of the character data
must also be updated. Table 20 contains VRAM structure and memory mapping.
512 Character
Set
Color Index Register
D7 D6 D5 D4 D3 D2 D1 D0
CLR_IDX: 09h Bank C
P[8:0] = character code
C[2:0] = character color
VRAM D[11:0] ^{11 10 9 8}
(4+8=12-bit word) _{P8 C2 C1 C0}
7 6 5 4 3 21 0
P7 P6 P5 P4 P3 P2 P1 P0
Character
color
Character code
Character Information
Figure 15 VRAM Data Path for 512 Character Set
PS001301-0800