MPC8280 datasheet(288/1386 Pages) FREESCALE

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The 60x Bus

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

8-12

Freescale Semiconductor

will cancel an active reservation during a snoop hit in the reservation

•

A non-processor read can cause the internal processor to invalidate the

corresponding cache line if it exists.

8.4.3.2

Transfer Code Signals TC[0–2]

The transfer code signals, TC[0–2], provide supplemental information about the corresponding address

(mainly regarding the source of the transaction). Note that TCx signals can be used with the TT[0–4] and

TBST to further define the current transaction.

8.4.3.3

TBST and TSIZ[0–3] Signals and Size of Transfer

As shown in Table 8-4, the transfer size signals (TSIZ[0–3]) and the transfer burst signal (TBST) together

indicate the size of the requested data transfer. These signals can be used with address bits A[27–31] and

the device port size to determine which portion of the data bus contains valid data for a write transaction

or which portion of the bus should contain valid data for a read transaction.

The MPC8280 uses four double word burst transactions for transferring cache blocks. For these

transactions, TSIZ[0–3] are encoded as 0b0010, and address bits A[27–28] determine which double-word

is sent first.

The MPC8280 supports critical-word-first burst transactions (double-word-aligned) from the processor.

The MPC8280 transfers the critical double word of data first, followed by the double words from

increasing addresses, wrapping back to the beginning of the eight-word block as required.

Table 8-3. Transfer Code Encoding for 60x Bus

TC[0–2]

60x Bus

Read

Write

000

Core data transaction

Any write

001

Core touch load

—

010

Core instruction fetch

—

011

Reserved

—

100

101

Reserved

110

DMA function code 0

111

DMA function code 1

Table 8-4. Transfer Size Signal Encoding

TBST

TSIZ[0–3]

Transfer Size

Comments

Source

Negated

0 0 0 1

1 Byte

Byte

Core and DMA

Negated

0 0 1 0

2 Bytes

Half word

Core and DMA

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