VIDC20 Data Sheet
1.2 Major Features
1.2.1 Flexible Video System
VIDC20 contains 296 write-only registers which offer a high degree of flexibility to the system programmer. 256 of these are used as the 28-bit video palette entries. These are programmed via an auto-incrementing address pointer. The remaining registers are specific control registers and allow the user to program the display parameters.
1.2.2 Hardware Cursor
VIDC20 has a hardware cursor for all its display modes - HiRes, Interlace and LCD display modes. By offering cursor support on chip the designer benefits in terms of speed and lower software overhead, resulting in an improved look and feel. The cursor is 32 pixels wide and any number of pixels high and can be displayed in 4 colours including transparent from its own 28 bit wide palette. In this way a cursor of any shape and size can be defined within the 32 pixel wide limit.
1.2.3 Palette
VIDC20 has a 28-bit wide 256-entry palette where each entry uses 8-bits for Red, 8 for Green and 8 for Blue, and 4 bits for external data. These external bits may be used outside the chip for a variety of purposes such as supremacy, fading, Hi-Res and LCD driving.
Look Up Tables (LUT) allow for logical to physical translation and gamma correctionThe Red Green and Blue LUTs each drive their respective DACs, and the Ext LiJT is normally configured to drive the 4 bit output port.
There are three 8-bit linear monotonic DACs (Red, Green and Blue) which give a total of 16 M possible colors. The DACs are designed to operate upto 100 MHz and drive doubly-terminated 75Q lines directly.
1.2.4 Pixel Clock
VIDC20 is capable of generating a display at any pixel rate up to 100MHz. The pixel dock may be selected from one of 3 sources, and then the selected frequency of this clock may be further divided down by a factor of between 1 and 8.
VIDC20 contains an on-chip phase comparator which, when used in conjunction with an external Voltage Controlled Oscillator (VCO), form a Phase Locked Loop. This configuration allows a single reference dock to generate all the required frequencies for any display mode thus obviating the need for multiple external crystals.
1.2.5 Display Modes
Irrespective of the memory configuration used, VIDC20 is capable of many different display formats. In addition to the normal linear CRT display, VIDC20 can generate a true interlaced display, or can generate a display suitable for either very high resolution displays, single or dual-panel LCDs.
For CRT displays, VIDC20 is capable of operating in a variety of pixel modes - 1,2,4,8,16,32 bits/pixel. VIDC20 can also directly drive LCD displays in 1,2 or 4 bits per pixel via an internal 16-level grey scaler. The grey s<aler algorithm adopted is patented.