MPC823 datasheet(67/74 Pages) MOTOROLA

67 / 74 page

Communication Processor Module

MOTOROLA

MPC823 REFERENCE MANUAL

16-445

W—Wrap (Final Buffer Descriptor in Table)

0 = This is not the last buffer descriptor in the RX buffer descriptor table.

1 = This is the last buffer descriptor in the RX buffer descriptor table. After this buffer

is used, the communication processor module receives incoming data into the first

buffer descriptor that RBASE points to in the table. The number of RX buffer

descriptors in this table is programmable and determined only by the W bit and

overall space constraints of the dual-port RAM.

I—Interrupt

No interrupt is generated after this buffer is filled.

The RXB bit in the SPIE register is set when this buffer is completely filled by the

communication processor module, indicating the need for the core to process the

buffer. The RXB bit can cause an interrupt if it is enabled.

CM—Continuous Mode

This bit is valid only when the serial peripheral interface is in master mode. In slave mode,

it must be written as a zero.

0 = Normal operation.

1 = The E bit is not cleared by the communication processor module after this buffer

descriptor is closed, thus allowing the associated data buffer to be automatically

overwritten next time the communication processor module accesses this buffer

descriptor. This allows continuous reception from an SPI slave into one buffer for

autoscanning of a serial A/D peripheral with no core overhead.

L—Last

This bit is set by the serial peripheral interface when the buffer is closed because the

SPISEL pin was negated. This only occurs when the serial peripheral interface is in slave

mode. Otherwise, the ME bit is set. The serial peripheral interface writes this bit after the

received data is placed into the associated data buffer.

0 = This buffer does not contain the last character of the message.

1 = This buffer contains the last character of the message.

OV—Overrun

This bit indicates that a receiver overrun has occurred during reception. This can only occur

when the serial peripheral interface is in slave mode. The serial peripheral interface writes

this bit after the received data is placed into the associated data buffer.

ME—Multimaster Error

This bit indicates that this buffer is closed because the SPISEL pin was asserted when the

serial peripheral interface was in master mode. This indicates a synchronization problem

between multiple masters on the SPI bus. The serial peripheral interface writes this bit after

the received data is placed into the associated data buffer.

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