Instruction manual

1.1 System Description: 300 Models
Figure 1 is a functional block diagram of the DEC 3000 AXP 300 models.
Numbers along communication lines indicate their bus width.
Major system components are:
• CPU:
A DECchip 21064–AA CPU, including on-chip 8 KB instruction and 8 KB
data caches, and a 64 KB (8 KB) serial boot ROM. Section 2.5 discusses CPU
registers that must be assigned specific values at startup.
• Cache:
A module-level write-back backup cache, or Bcache. The Bcache contains 256
KB, 32-byte blocks.
The cache tags are parity-protected, with separate parity bits for the address
and control sections. The control section has a dirty bit and a valid bit. The
valid bit is always set since the Bcache is initialized on power up with all
valid memory blocks. During system operation, the write-update protocol
used during DMA to maintain cache coherency assures that the Bcache blocks
must never be invalidated.
Section 2.6 describes Bcache tag space.
Section 10.1 describes the Bcache as a source of errors and interrupts.
Section 11.2 describes Bcache initialization.
• Memory Banks:
16 MB - 256 MB system memory, longword-parity protected, consisting of up
to four memory banks, each one of which must be populated by two SIMMS
of the same type. Using 1M x 4 DRAMs, the minimum memory size is 16
MB. Using 4M x 4 DRAMs, the maximum memory size is 256 MB. System
memory is longword parity-protected.
Section 2.2 discusses memory and I/O addressing; Section 3.2.3 discusses the
Memory Configuration Register (MCR).)
• TURBOchannel Interface:
A 12.5 MHz TURBOchannel interface for I/O, which is controlled by a
TURBOchannel ASIC. Section 3.2 discusses I/O Control and Status Registers.
Section 9.4 discusses TURBOchannel I/O programming. 300 models do not
support block-mode write operations.
• Graphics Subsystem
An 8-plane (2D) color graphics subsystem, called the CXTurbo, which is
connected to the TURBOchannel. The SFB (smart frame buffer) ASIC
controls this subsystem, which supports an 8-plane color monitor in the
resolution/refresh rate combinations of:
1024 x 768 @ 72 Hz (300L model)
1280 x 1024 @ 72 Hz (300, 300X, and 300LX models)
The CXTurbo is different from other TURBOchannel devices, in that it is
operated at the full TURBOchannel speed of 25 MHz and is accessible only in
dense I/O space. Appendix A discusses the use of dense and sparse I/O space
in the DEC 3000 AXP.
Chapter 6 describes the CXTurbo graphics subsystem.
1–2 Introduction to the DEC 3000 Models 300/400/500/600/700/800/900 AXP