MPC8280 datasheet(497/1386 Pages) FREESCALE

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Memory Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

11-77

11.6.4.1.3

General-Purpose Signals (G

xTx, GOx)

The general-purpose signals (GPL[1–5]) each have two bits in the RAM word that define 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 specified 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.

11.6.4.1.4

Loop Control

The LOOP bit in the RAM word (bit 24) specifies the beginning and end of a set of UPM RAM words that

are to be repeated. The first 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 field shown in Table 11-37..

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.

11.6.4.1.5

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 11-36.

Special care must be taken in the following cases:

•

When UTA and REDO are set together, PSDVAL is asserted the number of times specified 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.

Figure 11-79 shows an example of REDO use.

Table 11-37. M

xMR Loop Field Usage

Request Serviced

Loop Field

Read single-beat cycle

RLFx

Read burst cycle

RLFx

Write single-beat cycle

WLFx

Write burst cycle

WLFx

Refresh timer expired

TLFx

RUN

command

RLFx

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