22-14
MPC860 PowerQUICC UserÕs Manual
MOTOROLA
Part V. The Communications Processor Module
core (the buffer is empty). After using a descriptor, the CP clears E (not empty) and does
not reuse a BD until it has been processed by the core. However, in continuous mode (CM),
E remains set. When the CP discovers a descriptorÕs W bit set (indicating it is the last BD
in the circular BD table), it returns to the beginning of the table when it is time to move to
the next buffer.
22.3 SCC Parameter RAM
Each SCC parameter RAM area begins at the same offset from each SCC base area. The
protocol-speciÞc portions of the SCC parameter RAM are discussed in the speciÞc protocol
descriptions and the part that is common to all SCC protocols is shown in Table 22-4.
Some parameter RAM values must be initialized before the SCC can be enabled. Other
values are initialized or written by the CP. Once initialized, most parameter RAM values do
not need to be accessed because most activity centers around the descriptors rather than the
parameter RAM. However, if the parameter RAM is accessed, note the following:
¥
Parameter RAM can be read at any time.
¥
Tx parameter RAM can be written only when the transmitter is disabledÑafter a
STOP
TRANSMIT
command and before a
RESTART
TRANSMIT
command or after the
buffer/frame Þnishes transmitting after a
GRACEFUL
STOP
TRANSMIT
command and
before a
RESTART
TRANSMIT
command.
¥
Rx parameter RAM can be written only when the receiver is disabled. Note the
CLOSE
RX
BD
command does not stop reception, but it does allow the user to extract
data from a partially full Rx buffer.
¥
See Section 22.3.7, ÒReconÞguring the SCCs.Ó
Table 22-4 shows the parameter RAM map for all SCC protocols. Boldfaced entries must
be initialized by the user.
Table 22-4. SCC Parameter RAM Map for All Protocols
Offset
1
Name
Width
Description
0x00
RBASE
Hword Rx/TxBD table base addressÑoffset from the beginning of dual-port RAM. The BD
tables can be placed in any unused portion of the dual-port RAM. The CP starts BD
processing at the top of the table. (The user deÞnes the end of the BD table by setting
the W bit in the last BD to be processed.) Initialize these entries before enabling the
corresponding channel. Erratic operations occur if BD tables of active SCCs overlap.
Values in RBASE and TBASE should be multiples of eight.
0x02
TBASE
Hword
0x04
RFCR
Byte
Rx function code. See Section 22.3.1, ÒFunction Code Registers (RFCR and TFCR).Ó
0x05
TFCR
Byte
Tx function code. See Section 22.3.1, ÒFunction Code Registers (RFCR and TFCR).Ó
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