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Part III. The Hardware Interface
10.6.4.1.3 General-Purpose Signals (GxTx, GOx)
The general-purpose signals (GPL[1Ð5]) each have two bits in the RAM word that deÞne
the logical value of the signal to be changed at the rising edge of T1 and/or at the rising edge
of T3. GPL0 offer enhancements beyond the other GPLx lines.
GPL0 can be controlled by an address line speciÞed in MxMR[G0CLx]. To use this feature,
set G0H and G0L in the RAM word. For example, for a SIMM with multiple banks, this
address line can be used to switch between banks.
10.6.4.1.4 Loop Control
The LOOP bit in the RAM word (bit 24) speciÞes the beginning and end of a set of UPM
RAM words that are to be repeated. The Þrst time LOOP = 1, the memory controller
recognizes it as a loop start word and loads the memory loop counter with the
corresponding contents of the loop Þeld shown in Table 10-36. The next RAM word for
which LOOP = 1 is recognized as a loop end word. When it is reached, the loop counter is
decremented by one.
Continued loop execution depends on the loop counter. If the counter is not zero, the next
RAM word executed is the loop start word. Otherwise, the next RAM word executed is the
one after the loop end word. Loops can be executed sequentially but cannot be nested.
Read single-beat cycle
Read burst cycle
Write single-beat cycle
Write burst cycle
Refresh timer expired
RUN
10.6.4.1.5 Repeat Execution of Current RAM Word (REDO)
The REDO function is useful for wait-state insertion in a long UPM routine that would
otherwise need too many RAM words. Setting the REDO bits of the RAM word to a
nonzero value to cause the UPM to reexecute the current RAM word up to three times,
according to Table 10-35.
Special care must be taken in the following cases:
¥ When UTA and REDO are set together, PSDVAL is asserted the number of times
speciÞed by the REDO function.
¥ When LOOP and REDO are set together, the loop mechanism works as usual and
the line is repeated according to the REDO function.
¥ LAST and REDO should not be set together.
¥ REDO should not be used within the exception routine.
10-76
Table 10-36. MxMR Loop Field Usage
Request Serviced
command
MPC8260 PowerQUICC II UserÕs Manual
Loop Field
RLFx
RLFx
WLFx
WLFx
TLFx
RLFx
MOTOROLA
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