Product Description

The Bt471, 476, and 478 are pin-compatible

and software-compatible RAMDACs de-

signed specifically for Personal System/2?-

compatible color graphics. The Bt476 is

also available in a 28-pin DIP package that

is pin compatible with the IMS? G176.

‘The Bt471 has a 256 x 18 color lookup ta-

ble with triple 6-bit video D/A converters.

The Bt478 has a 256 x 24 color lookup table

with triple 8-bit video D/A converters. It

may be configured for either 6-bit or 8-bit

D/A converter operation. The Bt476 is simi-

lar to the Bt471 but has no overlays, no pro-

grammable setup, and no sync information

on the analog outputs.

Additional features on the Bt471 and

Bt478 include 15 overlay registers that pro-

vide, for example, overlaying cursors, grids,

‘menus, and EGA emulation. Also supported

is sync generation on all three channels, a

programmable pedestal (0 or 7.5 IRE), and

use of either an external voltage or current

reference.

‘The Bt471/476/478 generates RS-343A-

compatible video signals into a doubly-

terminated 75 Q load.

Note: Personal System/2? and PS/2? are

registered trademarks of IBM. IMS? is a

registered trademark of Inmos Limited.

Distinguishing Features

+ Personal System/2? Compatibility

+ 80,66, 50, 35 MHz Operation

Triple 6-bit or 8-bit D/A Converters

+ 256-Word Color Palette RAM

+ RS-343A-Compatible Outputs

* 15 Overlay Registers (Bt471/478)

+ Sync on All Three Channels

(Bt471/478)

+ Programmable Pedestal (Bt471/478)

+ External Voltage or Current

Reference

+ Standard MPU Interface

+ +5 V CMOS Monolithic

Construction

?+ 44-pin PLCC or 28-pin DIP Package

Applications

+ High-Resolution Color

Graphics

+ CAE/CAD/CAM

+ Image Processing

+ Instrumentation

+ Desktop Publishing