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Serial Management Controllers (SMCs)
7-300
MC68360 USER’S MANUAL
MOTOROLA
1 = The data buffer associated with this BD is empty, or reception is currently in
progress. This Rx BD and its associated receive buffer are owned by the CP. Once
the E-bit is set, the CPU32+ core should not write any fields of this Rx BD.
Bits 14, 11, 10, 8–2, 0—Reserved
W—Wrap (Final BD in Table)
0 = This is not the last BD in the Rx BD table.
1 = This is the last BD in the Rx BD table. After this buffer has been used, the CP will
receive incoming data into the first BD in the table (the BD pointed to by RBASE).
The number of Rx BDs in this table is programmable and is determined only by the
W-bit and the overall space constraints of the dual-port RAM.
I—Interrupt
0 = No interrupt is generated after this buffer has been filled.
1 = The RX bit in the event register will be set when this buffer has been completely
filled by the CP, indicating the need for the CPU32+ core to process the buffer. The
RX bit can cause an interrupt if it is enabled.
CM—Continuous Mode
0 = Normal operation.
1 = The E-bit is not cleared by the CP after this BD is closed, allowing the associated
data buffer to be overwritten automatically when the CP next accesses this BD.
However, the E-bit will be cleared if an error occurs during reception, regardless of
the CM bit.
The following status bit is written by the CP after the received data has been placed into the
associated data buffer.
OV—Overrun
A receiver overrun occurred during message reception.
Data Length
The data length is the number of octets that the CP has written into this BD’s data buffer.
It is written only once by the CP as the buffer is closed.
NOTE
The actual amount of memory allocated for this buffer should be
greater than or equal to the contents of the MRBLR.
Rx Data Buffer Pointer
The receive buffer pointer, which always points to the first location of the associated data
buffer, must be even. The buffer may reside in either internal or external memory.
7.11.10.12 SMC TRANSPARENT TRANSMIT BUFFER DESCRIPTOR (TX BD). Data
is
presented to the CP for transmission on an SMC channel by arranging it in buffers refer-
enced by the channel’s Tx BD table. The CP confirms transmission or indicates error con-
ditions using the BDs to inform the processor that the buffers have been serviced.