Description - IBM RT Series Hardware Reference Manual

Description
The Advanced Color Graphics Display Adapter attaches to the I/O channel and drives a 14-inch
color display at a 46 Hz (frame rate) or 92 Hz (field rate) interlace refresh rate. The adapter
provides a 256K-byte bit map that is translated to the screen as 720 pels horizontally by 512 pels
vertically, at 4 bits per pel. A 4-plane bit map (64K-byte each plane) is provided from which 16
colors are picked from a 64 color palette.
The adapter includes several hardware performance assists, including a write mask to protect bit
fields within a byte, a barrel shifter to rotate bits within a byte, and a logic unit to combine source
bytes before they are written into the bit map. In addition, a plane select register and foreground or
background register are provided as a means to select individual planes or all planes for update with
each system access using preprogrammed foreground or background color data. A 4-bit to 6-bit
video lookup Random Access Memory (RAM), writeable from the system, is also provided for the
selection of 16 usable colors from a palette of 64 available colors, and is represented to the monitor
using 2-bits per primary color (red, red intense, green, green intense, blue and blue intense).
Figure 1 on page 2 is a block diagram of the Advanced Color Graphics Display Adapter.
Advanced Color Graphics Display Adapter 1