Specifications

CHAPTER 2
Hardware Design
22 Video System
Video System 2
The 12” and 7” cards in conjunction with video cards provide a complete video system
to support PC video. This system consists of a VGA controller (ATI 264CT) with an
integrated CLUT, a digital-to-analog converter (DAC), and a clock generator.
PC video out is supported not only on VGA monitors but also on Macintosh
fixed-frequency monitors that emulate VGA modes. This means you can use your
existing Macintosh monitors in a shared configuration for both Macintosh and PC video.
Connecting the Monitor 2
Video output from the 12” and 7” cards can be displayed on a monitor that is shared
with the host Macintosh computer or, with some CPUs, on a dedicated monitor.
“Loop-Back Video Support” beginning on page 30 and “GIMO Support for Video
Output” beginning on page 28 provide detailed information on this subject. If you are
using a shared monitor, you can switch from Macintosh to PC screen using a
programmable key sequence.
Monitors Supported 2
The VGA controller/accelerator provides complete VGA compatibility for modes 0–7
and D–13h. Both cards come with 1 MB of video DRAM installed. The 12” card has two
additional DRAM sockets that allow you to add another 1 MB of video DRAM. The
1 MB DRAM enables a 32-bit data path, and the additional memory enables a 64-bit data
path. This additional width in the data path supports additional color depths, as
indicated in Table 2-4.
The ATI 264CT senses which monitor is attached whenever you use the loopback cable
to connect the monitor to the cards. This is true even in shared-monitor mode. When you
use the GIMO connector to connect the monitor, the Macintosh host computer
determines the monitor for the PC and makes the appropriate adjustments.