Section 1.1, "Overview - Motorola PowerPC 603 Hardware Specifications

1.1 Overview
This section describes the features of the 603 and describes briefly how those units interact.
The 603 is the first low-power implementation of the PowerPC microprocessor family of RISC
microprocessors. The 603 implements the PowerPC architecture as it is specified for 32-bit addressing,
which provides 32-bit effective (logical) addresses, integer data types of 8, 16, and 32 bits, and floating-
point data types of 32 and 64 bits (single-precision and double-precision). For 64-bit PowerPC
implementations, the PowerPC architecture provides additional 64-bit integer data types, 64-bit addressing,
and related features.
The 603 provides four software controllable power-saving modes. Three of the modes (the doze, nap, and
sleep modes) are static in nature, and progressively reduce the amount of power dissipated by the processor.
The fourth is a dynamic power management mode that causes the functional units in the 603 to
automatically enter a low-power mode when the functional units are idle without affecting operational
performance, software execution, or any external hardware.
The 603 is a superscalar processor capable of issuing and retiring as many as three instructions per clock.
Instructions can execute out of order for increased performance; however, the 603 makes completion appear
sequential.
The 603 integrates five execution units—an integer unit (IU), a floating-point unit (FPU), a branch
processing unit (BPU), a load/store unit (LSU), and a system register unit (SRU). The ability to execute five
instructions in parallel and the use of simple instructions with rapid execution times yield high efficiency
and throughput for 603-based systems. Most integer instructions execute in one clock cycle. The FPU is
pipelined so a single-precision multiply-add instruction can be issued every clock cycle.
The 603 provides independent on-chip, 8-Kbyte, two-way set-associative, physically addressed caches for
instructions and data and on-chip instruction and data memory management units (MMUs). The MMUs
contain 64-entry, two-way set-associative, data and instruction translation lookaside buffers (DTLB and
ITLB) that provide support for demand-paged virtual memory address translation and variable-sized block
translation. The TLBs and caches use a least recently used (LRU) replacement algorithm. The 603 also
supports block address translation through the use of two independent instruction and data block address
translation (IBAT and DBAT) arrays of four entries each. Effective addresses are compared simultaneously
with all four entries in the BAT array during block translation. In accordance with the PowerPC architecture,
if an effective address hits in both the TLB and BAT array, the BAT translation takes priority.
The 603 has a selectable 32- or 64-bit data bus and a 32-bit address bus. The 603 interface protocol allows
multiple masters to compete for system resources through a central external arbiter. The 603 provides a
three-state coherency protocol that supports the exclusive, modified, and invalid cache states. This protocol
is a compatible subset of the MESI (modified/exclusive/shared/invalid) four-state protocol and operates
coherently in systems that contain four-state caches. The 603 supports single-beat and burst data transfers
for memory accesses; it also supports both memory-mapped I/O and direct-store addressing.
The 603 uses an advanced, 3.3-V CMOS process technology and maintains full interface compatibility with
TTL devices.
2 603 Hardware Specifications