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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_01.fm.(1.2)
March 27,2006
PowerPC 750GX Overview
Page 37 of 377
The system interface supports address pipelining, which allows the address tenure of one transaction to
overlap the data tenure of another. The 750GX can support up to five outstanding transactions on the bus,
including up to one snoop copyback, up to four loads, and up to four stores. The extent of the pipelining
depends on external arbitration and control circuitry. Similarly, the 750GX supports split-bus transactions for
systems with multiple potential bus masters—one device can be master of the address bus while another is
master of the data bus. Allowing multiple bus transactions to occur simultaneously increases the available
bus bandwidth for other activity.
The 750GX’s clocking structure supports a wide range of processor-to-bus clock ratios.
1.2.7 Signals
The 750GX’s signals are grouped as follows:
Figure 1-3. System Interface
Address arbitration The 750GX uses these signals to arbitrate for address-bus mastership.
Address start This signal indicates that a bus master has begun a transaction on the address
bus.
Address transfer These signals include the address bus and are used to transfer the address.
Transfer attribute These signals provide information about the type of transfer, such as the transfer
size and whether the transaction is burst, write-through, or caching-inhibited.
Address termination These signals are used to acknowledge the end of the address phase of the trans-
action. They also indicate whether a condition exists that requires the address
phase to be repeated.
Data arbitration The 750GX uses these signals to arbitrate for data-bus mastership.
Data transfer These signals include the data bus and are used to transfer the data.
Data termination These signals are required after each data beat in a data transfer. In a single-beat
transaction, a data termination signal also indicates the end of the tenure. In burst
accesses, data termination signals apply to individual beats and indicate the end of
the tenure only after the final data beat.
Address Arbitration
Address Start
Address Transfer
Transfer Attribute
Address Termination
Clocks
Data Arbitration
Data Transfer
Data Termination
Test and Control
Interrupt
VDD VDD (I/O)
750GX
Processor Status/Control