Bt457/Bt458
125 MHz/135 MHz/165 MHz Monolithic CMOS 256 Color Palette
RAMDAC
The Bt457 and Bt458 are pin- and software-compatible RAMDACs designed specifically
for high-performance, high-resolution color graphics. The architecture enables a display
of 1280 x 1024 bit-mapped color graphics (up to 8 bits per pixel plus up to 2 bits of
overlay information). This minimizes the use of costly ECL interfacing, because most of
the high-speed (pixel clock) logic is contained on-chip. The multiple pixel ports and
internal multiplexing enable TTL-compatible interface (up to 32 MHz) to the frame
buffer, while maintaining the 165 MHz video data rates required for sophisticated color
graphics.
The Bt457 is a single-channel version of the Bt458 and has a 256 x 8 color lookup
table with a single 8-bit video D/A converter. It includes a PLL output to enable subpixel
synchronization of multiple Bt457s.
On-chip features include programmable blink rates, bit plane masking and blinking,
color overlay capability, and a dual-port color palette RAM.
Distinguishing Features
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165, 135, 125, 110, 80 MHz
operation
4:1 or 5:1 input mux
256-word dual-port color palette
Four dual-port overlay registers
RS-343A-compatible outputs
Bit plane read and blink masks
Standard MPU interface
84-pin PLCC or PGA package
+5 V CMOS monolithic
construction
Applications
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Functional Block Diagram
CLOCK*
CLOCK
VAA
Load
Control
LD*
GND
MUX
Control
FSADJUST
VREF
COMP
Blink
Control
4(8)
P[7:0] 40
(A-E)
40
40
8
Latch
OL[1,0] 10
(A-E)
Read Blink
Mask Mask
Latch
10
10
256 X 12
(24)
Color
Palette
8
MUX
2
High-resolution color graphics
CAE/CAD/CAM
Image processing
Video reconstruction
4 x 12
(24)
Overlay
2
4(8)
4(8)
IOR (N/C)
IOG (IOUT)
IOB (PLL)
SYNC*
BLANK*
Bus Control
ADDR Reg
R
G
B
4(8)
8
CE* R/W CO
Data Sheet
C1
D[7:0]
457-8_001
CLOCK
L45801 Rev. N
September 2, 1999
