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PDF BT481A Data sheet ( Hoja de datos )
| Número de pieza | BT481A | |
| Descripción | 110 Mhz / 256 Word Color Palette / 24 Bit True Color Power Down RAMDAC | |
| Fabricantes | Brooktree | |
| Logotipo |  |
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Bt481A
110 MHz 256-Word Color Palette 15-, 16-, and
24-Bit True Color Power-Down RAMDAC
Designed specifically for high-performance color graphics, the Bt481A RAM-
DAC supports three true-color modes: 15-bit (5:5:5, 32 K colors) TARGA for-
mat, 16-bit (5:6:5, 65 K colors) XGA format, and 24-bit BGR (8:8:8, RGB/
BGR, 16.8 M colors) true-color format. It also supports 8-bit pseudo-color for-
mat (256 colors).
The Bt481A has a 256 x 18 (24) lookup table RAM, 15 x 8 (24) overlay reg-
isters, and triple 8-bit D/A converters. Both 6- and 8-bit color modes are sup-
ported.
A power-down mode is available on the Bt481A to reduce power require-
ments when the analog outputs are not used. This is useful in laptop computer
systems that require the option to drive an external RGB monitor.
The Bt481A has on-chip analog output comparators to simplify diagnostics
and debugging, with the result output onto the SENSE* pin. Also included is an
on-chip voltage reference to simplify use of the device.
The Bt481A generates RS-343-compatible video signals into a doubly termi-
nated load.
Functional Block Diagram
VAA GND
VREF IREF
CLOCK
P[7:0]
SYNC*
BLANK*
OL0–OL3
SETUP
TRUECOL*
1.2 V
Reference
Amplifier
8
Latch
4
Pixel
Read
Mask Reg
Overlay
Mask
Reg
256 x 18 (24)
Color
Palette
15 x 18 (24)
Overlay
Color
Palette
6 (8)
6 (8)
6 (8)
DAC
DAC
DAC
Compare
ADDR Reg
8
RG B
6 (8) 6 (8) 6 (8)
BUS Control
OPA
COMP
IOR
IOG
IOB
SENSE*
6*/8
D[7:0]
RD* WR* RS[2:0]
Distinguishing Features
• 110 MHz Operation
• Supports 8:8:8:8, 24-bit true color
and VGA overlay
• Supports 8:8:8 24-bit RGB/BGR
selectable true-color format
• Supports 5:6:5 XGA true-color
format
• Supports 5:5:5 TARGA true-color
format
• Replaces Bt471/475/476/477/478
which are pin compatible
• Power-on reset for internal
registers
• Power-down mode
• Antisparkle circuitry
• Analog output conparators
• Triple 6-bit (8-bit) D/A converters
• 256 x 18 (24) color palette RAM
• 15 x 18 (24) overlay registers
• Optional internal voltage reference
• Programmable pedestal
• Sync on all three channels
• Standard MPU interface
• 44-pin PLCC package
Applications
• High-resolution color graphics
• CAE/CAD/CAM
• Image processing
• Instrumentation
• Desktop publishing
• Laptop computers
Brooktree® Brooktree Corporation • Rockwell Semiconductor Systems, Inc. • 9868 Scranton Road • San Diego, CA 92121-3707
619-452-7580 • 1-800-2-BT-APPS • FAX: 619-452-1249 • Internet: [email protected] • L481A_C
1 page  
Bt481A
110 MHz 256-Word Color Palette 15-, 16-, and 24-Bit True Color Power-Down RAMDAC
LIST OF FIGURES
List of Figures
Figure 1. Pinout Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Figure 2. Detailed Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Figure 3. Bt481A Internal VREF and DAC Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Figure 4. RS-343A Composite Video Output Waveforms (SETUP = 7.5 IRE) . . . . . . . . . . . . . . . . 15
Figure 5. RS-343A Composite Video Output Waveforms (SETUP = 0 IRE) . . . . . . . . . . . . . . . . . . 16
Figure 6. PS/2 Composite Video Output Waveforms (SETUP = 0 IRE) . . . . . . . . . . . . . . . . . . . . . 17
Figure 7. Sample Layout Showing Power and Ground Plane Isolation Gaps . . . . . . . . . . . . . . . . . 22
Figure 8. Typical Connection Diagram and Parts List (Internal Voltage Reference) . . . . . . . . . . . . 23
Figure 9. Typical Connection Diagram and Parts List (External Voltage Reference) . . . . . . . . . . . 24
Figure 10. Typical Connection Diagram and Parts List (External Current Reference) . . . . . . . . . . . 25
Figure 11. MPU Read/Write Timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Figure 12. Video Input/Output Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Figure 13. 15-, 16-, and 24-Bit-Per-Pixel (RGB) Timing, Dual-Edge Clock Mode . . . . . . . . . . . . . . . 40
Figure 14. 15-, 16-, and 32-Bit-Per-Pixel (BGR) Timing, Dual-Edge Clock Mode . . . . . . . . . . . . . . . 41
Figure 15. 15-, 16-, and 24-Bit-Per-Pixel (RGB) Timing, Single-Edge Clock Mode . . . . . . . . . . . . . 42
Figure 16. 15-, 16-, and 24-Bit-Per-Pixel (BGR) Timing, Single-Edge Clock Mode . . . . . . . . . . . . . 43
Figure 17. 44-Pin Plastic J-Lead (PLCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Brooktree®
L481A_C
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5 Page 
Bt481A
110 MHz 256-Word Clor Palette 15-, 16-, and 24-Bit True Color Power-Down RAMDAC
FUNCTIONAL DESCRIPTION
MPU Interface
MPU Interface
As illustrated in the detailed block diagram (Figure 2), the Bt481A supports a stan-
dard MPU bus interface, allowing the MPU direct access to the color palette RAM
and overlay color registers.
The RS[2:0] select inputs specify whether the MPU is accessing the address
register, color palette RAM, overlay registers, or read mask register, as shown in
Table 2. The 8-bit address register addresses the color palette RAM and overlay
registers, eliminating the requirement for external address multiplexers. ADDR0
corresponds to D[0] and is the least significant bit (see Table 3).
Table 2. Control Input Truth Table
RS[2]
RS[1]
RS[0]
000
011
001
010
100
111
101
110
Addressed by MPU
Address Register (Palette Write Mode)
Address Register (Palette Read Mode)
Color Palette RAM
Pixel Read Mask Register
Address Register (Overlay Write Mode)
Address Register (Overlay Read Mode)
Overlay Registers
Command Register A
Table 3. Address Register (ADDR) Operation
Value
ADDRa, (Counts Modulo 3)
ADDR[7:0] (Counts Binary)
00
01
10
$00–$FF
0000 0000
0000 0001
:
0000 1111
RS[2] RS[1] RS[0]
001
101
101
:::
101
Addressed by MPU
Red Value
Green Value
Blue Value
Color Palette RAM
Reserved
Overlay Color 1
:
Overlay Color 15
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L481A_C
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