TLC34075A

The TLC34075A Video Interface Palette (VIP) is designed to provide lower system cost with a higher level of integration by incorporating all the high-speed timing, synchronizing, and multiplexing logic usually associated with graphics systems into one device, thus greatly reducing chip count. Since all high-speed signals of TLC34075A (excluding the clock source) are contained on-chip, RF noise considerations are simplified.

Maximum flexibility of TLC34075A is provided through the pixel multiplexing scheme, which allows for 32-, 16-, 8-, and 4-bit pixel buses to be accommodated without any circuit modification. This enables the system to be easily reconfigured for varying amounts of available video RAM. Data can be split into 1, 2, 4, or 8 bit planes. The TLC34075A is software-compatible with the INMOS IMSG176/8 and Brooktree BT476/8 color palettes.

The TLC34075A features a separate VGA bus that allows data from the feature connector of most VGA-supported personal computers to be fed directly into the palette without the need for external data multiplexing. This allows a replacement graphics board to remain downward compatible by utilizing the existing graphics circuitry often located on the motherboard. The TLC34075A also provides a true color mode in which 24 (3 by 8) bits of color information are transferred directly from the pixel port to the DACs. This mode of operation supplies an overlay function using the 8 remaining bits of the pixel bus.

The TLC34075A has a 256-by-24 color lookup table with triple 8-bit video D/A converters capable of directly driving a doubly terminated 75-W line. Sync generation is incorporated on the green output channel. HSYNC and VSYNC are fed through the device and optionally inverted to indicate screen resolution to the monitor. A palette page register provides the additional bits of palette address when 1, 2, or 4 bit planes are used. This allows the screen colors to be changed with only one MPU write cycle.

Clocking is provided through one of four or five inputs (3 TTL- and either 1 ECL- or 2 TTL-compatible) and is software selectable. The video and shift clock outputs of TLC34075A provide a software-selected divide ratio of the chosen clock input.

The TLC34075A can be connected directly to the serial port of VRAM devices, eliminating the need for any discrete logic. Support for split shift register transfers is also provided.

The TLC34075A is an optimized version of the original TLC34075 video interface palette. Because all of the critical speed paths have been strengthened on the device, a slightly higher IDD current specification is required. The new specification also includes revised SCLK/VCLK timing and a clock counter reset function.