Motorola MPC8260 User Manual

26-8

MOTOROLA

Certain parameter RAM values must be initialized before the SMC is enabled. Other values
are initialized or written by the CP. Once values are initialized, software typically does not
need to update them because activity centers mostly around transmit and receive BDs rather
than parameter RAM. However, note the following:

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Parameter RAM can be read at any time.

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Values that pertain to the SMC transmitter can be written only if SMCMR[TEN] is 
zero or between the 

STOP

 

TRANSMIT

 and 

RESTART

 

TRANSMIT

 commands. 

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Values for the SMC receiver can be written only when SMCMR[REN] is zero, or, if 
the receiver is previously enabled, after an 

ENTER

 

HUNT

 

MODE

 command is issued 

but before the 

CLOSE

 

RXBD

 command is issued and REN is set.

Each SMC channel has four receive buffers (RFCRn) and four transmit buffers (TFCRn).
The function code registers contain the transaction speciÞcation associated with SDMA
channel accesses to external memory. Figure 26-4 shows the register format.

Bit

0

1

2

3

4

5

6

7

Field

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R/W

R/W

Address

SMC base + 0x04 (RFCR)/SMC base + 0x05 (TFCR)

0Ð1

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Reserved, should be cleared.

2

Global access bit
0 Disable memory snooping
1 Enable memory snooping

3Ð4

Byte ordering. Selects byte ordering of the data buffer. 
00 The DEC/Intel convention (swapped operation or little-endian). The transmission order of bytes 

within a buffer word is opposite of Motorola mode. (32-bit port size memory only).

01 PowerPC little-endian. As data is sent onto the serial line from the buffer, the LSB of the buffer 

double word contains data to be sent earlier than the MSB of the same double word. 

1x Motorola (big-endian) byte ordering (normal operation). As data is sent onto the serial line from the 

buffer, the MSB of the buffer word contains data to be sent earlier than the LSB of the same word.

5

Transfer code 2. Contains the transfer code value of TC[2], used during this SDMA channel memory 
access. TC[0Ð1] is driven with a 0b11 to identify this SDMA channel access as a DMA-type access.

6

Data bus indicator.
0 Use 60x bus for SDMA operation.
1 Use local bus for SDMA operation. 

7

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Reserved, should be cleared.