Instruction manual

6
CXTurbo Graphics Subsystem: 300/500 Models
The 300 and 500 models feature the CXTurbo graphics subsystem, although small
differences exist between the 300 model and 500 model CXTurbo. The CXTurbo
graphics subsystem provides 8-plane graphics with enhanced hardware features
common to graphics accelerators. The graphics subsystem nonetheless remains
a TURBOchannel subsystem with one ASIC for hardware control. The CXTurbo
graphics system consists of the following components:
• Smart frame buffer (SFB) ASIC—184-pin PQFP
• Video RAMs—16 256Kx4 split shifter VRAMs
• MUXes—connecting VRAMS to RAMDAC
• RAMDAC with cursor—Bt459 RAMDAC with 256 entry color map
• Crystal Oscillators:
1280x1024 @ 72 Hz—300, 300X, 300LX models
1024x768 @ 72 Hz—300L model
1280x1024 @ 66 Hz or 72 Hz (user selectable)—500 models
• System FEPROM—256 KB Flash memory
This chapter covers the following topics:
• Comparison of features (Section 6.1)
• CXTurbo address map (Section 6.2)
• Frame buffer control registers (Section 6.3)
• SFB (smart frame buffer) ASIC functions (Section 6.4)
• Bt459 RAMDAC (Section 6.5)
• System FEPROM (500 Models) (Section 6.6)
CXTurbo Graphics Subsystem: 300/500 Models 6–1