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