Vax 613 0S Instruction Manual download pdf (Page 100)

6.5 Bt459 RAMDAC

The CXTurbo option uses the Bt459 RAMDAC in conjunction with a clock

generator chip for sourcing the 8-plane RGB data. Below are details for writing

the RAMDAC color map and control registers. For more information on the

Bt459, see the manufacturer’s Bt459 RAMDAC Speciﬁcation.

The Bt459 supports a cursor function and three 256x8-bit color maps for its red,

green, and blue video DACs. In addition the Bt459 incorporates testability logic

that allows software to determine if the monitor is connected to the analog RGB

outputs, and if the DAC is functional.

To avoid unplanned signals in the video output, Bt459 is updated only during

the vertical synch period. Hardware does not support the Bt459’s overlay plane

feature; software must disable it.

The Bt459 supports only byte reads and writes. The Bt459 registers are therefore

longword-aligned in the SFB ASIC’s address space.

The Bt459’s register map is:

Address Register

300 Models

1.C21C.0000 Address register low byte [7:0]

1.C21C.0004 Address register high byte [15:8]

1.C21C.0008 Register addresses by address register

1.C21C.000C Color map loc addressed by address register

500 Models

1.E21C.0000 Address register low byte [7:0]

1.E21C.0004 Address register high byte [15:8]

1.E21C.0008 Register addresses by address register

1.E21C.000C Color map loc addressed by address register

The Bt459’s indirectly addressed register map is:

Address

Reg[15:0] Register

300 Models

020B Test register

020C Red signature register

020D Green signature register

020E Blue signature register

020F - 02FF Reserved

0300 Cursor command register

0301 Cursor (x) low register

0302 Cursor (x) high register

0303 Cursor (y) low register

6–20 CXTurbo Graphics Subsystem: 300/500 Models

1 2 ... 95 96 97 98 99 100 101 102 103 104 105 ... 343 344

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Vax 613 0S Instruction Manual Page 100