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User’s Manual
IBM PowerPC 750GX and 750GL RISC Microprocessor
gx_08.fm.(1.2)
March 27, 2006
Bus Interface Operation
Page 283 of 377
one, two, or eight beats depending on the size of the program transaction and the cache mode for the
address. For additional information about 32-bit data bus mode, see Section 8.6.1, 32-Bit Data Bus Mode, on
page 316.”
8.1.5 Direct-Store Accesses
The 750GX does not support the extended transfer protocol for accesses to the direct-store storage space.
The transfer protocol used for any given access is selected by the T bit in the MMU Segment Registers. If the
T bit is set, the memory access is a direct-store access. An attempt to access instructions or data in a direct-
store segment will result in the 750GX taking an instruction storage interrupt (ISI) or data-storage interrupt
(DSI) exception.
Figure 8-2. Timing Diagram Legend
A sampled condition (dot on high or low state) with multiple dependencies
Note: A bar over signal name indicates active low.
ap0
BR
ADDR+
qual BG
750GX output (while 750GX is a bus master)
750GX input (while 750GX is a bus master)
750GX output (grouped: here, address plus attributes)
750GX internal signal (inaccessible to the user, but used in diagrams to
clarify operations)
Compelling dependency—event will occur on the next clock cycle
Prerequisite dependency—event will occur on an undetermined subsequent
clock cycle
750GX tristate output or input
750GX nonsampled input
Signal with sample point
Timing for a signal had it been asserted (it is not actually asserted)