mpc604e Freescale Semiconductor, Inc, mpc604e Datasheet - Page 15

• Manufacturer Part Number: mpc604e
• Description: Powerpc 604e-tm Risc Microprocessor Technical Summary
• Manufacturer: Freescale Semiconductor, Inc

PowerPC 604e RISC Microprocessor Technical Summary
1.2.11 System Interface/Bus Interface Unit (BIU)
The 604e provides a versatile bus interface that allows a wide variety of system design options. The
interface includes a 72-bit data bus (64 bits of data and 8 bits of parity), a 36-bit address bus (32 bits of
address and 4 bits of parity), and sufficient control signals to allow for a variety of system-level
optimizations. The 604e uses one-beat and four-beat data transactions, although it is possible for other bus
participants to perform longer data transfers. The 604e clocking structure supports processor-to-bus clock
ratios of 1:1, 3:2, 2:1, 5:2, 3:1, and 4:1, as described in Section 1.2.12, “Clocking.” Note that support for
processor/bus clock ratios 5:2 and 4:1 is specific to the 604e and is not supported in the 604.
To support the changes in the clocking configuration, different precharge timings for the ABB, DBB,
ARTRY, and SHD signals are implemented internally by the processor. The precharge timings for ARTRY
and SHD can be disabled by setting HID0[7].
The 604e has the same pin configuration as the 604; however, on the 604e Vdd and AVdd must be tied to
2.5 Vdc and OVdd must be tied to 3.3 Vdc. The 604e uses split voltage planes, and for replacement
compatibility, 604/604e designs should provide both 2.5-V and 3.3-V planes and the ability to tie those two
planes together and disable the 2.5-V plane for operation with a 604.
In addition to the normal and data-streaming modes implemented on the 604, a no-DRTRY mode is
implemented on the 604e that improves performance on read operations for systems that do not use the
DRTRY signal. No-DRTRY mode makes read data available to the processor one bus clock cycle sooner
than in normal mode . In no-DRTRY mode, the DRTRY signal is no longer sampled as part of a qualified
bus grant.
The system interface is specific for each PowerPC processor implementation. The 604e system interface is
shown in Figure 4.
Four-beat burst-read memory operations that load an eight-word cache block into one of the on-chip caches
are the most common bus transactions in typical systems, followed by burst-write memory operations,
direct-store operations, and single-beat (noncacheable or write-through) memory read and write operations.
Additionally, there can be address-only operations, variants of the burst and single-beat operations (global
memory operations that are snooped and atomic memory operations, for example), and address retry
activity (for example, when a snooped read access hits a modified line in the data cache).
Memory accesses can occur in single-beat or four-beat burst data transfers. The address and data buses are
independent for memory accesses to support pipelining and split transactions. The 604e supports bus
pipelining and out-of-order split-bus transactions. In general, the bus-pipelining mechanism allows as many
ADDRESS TERMINATION
ADDRESS ARBITRATION
TRANSFER ATTRIBUTE
ADDRESS TRANSFER
ADDRESS START
ADDRESS
CLOCKS
Figure 4. System Interface
+3.3 V
Processor
PowerPC
604e
+2.5 V
DATA
DATA ARBITRATION
DATA TRANSFER
DATA TERMINATION
PROCESSOR STATE
TEST AND CONTROL
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