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4.5.6.2 MAXIMUM RECEIVE BUFFER LENGTH REGISTER (MRBLR). The MRBLR
for each SCC channel defines the maximum number of bytes that the IMP
will write to a buffer before moving to the next buffer. It must be set by the
user before data is received on that channel. Since only one maximum buffer
size is given per channel (and not for each buffer), this value must not exceed
the size of the smallest buffer linked to this channel's BD table.
NOTE
The MRBLR value should be greater than zero in all modes. In the
HDLC mode, the MRBLR should have an even value.
4.5.6.3 RECEIVER BUFFER DESCRIPTOR NUMBER (RBD#). The RBD# for each
SCC channel defines the next BD to which the receiver will move data when
it is in the IDLE state or defines the current BD during frame processing. The
ROB# is the BD offset from the SCC base in the Rx BD table. For Rx BD 0,
RBD#=$00; for Rx BD 1, RBD#=$08, etc. Upon reset, the CP main controller
sets this register to zero. The user can change this register only after the
ENTER HUNT MODE command has been issued.
4.5.6.4 TRANSMIT BUFFER DESCRIPTOR NUMBER (TBD#). The TBD# for each
SCC channel defines the next BD from which the transmitter will move data
when it is in the IDLE state or defines the current BD during frame trans-
mission. The TDB# is the BD offset from the SCC base in the Tx BD table.
For Tx BD 0, TBD#=$40; for Tx BD 1, TBD#=$48, etc. Upon reset, the CP
main controller sets this register to $40. The user can change this register
only after the STOP TRANSMIT command has been issued.
4.5.7 SCC Initialization
4-28
After poweron reset, first program the function of the parallel 1/0 port pins
versus on-chip peripheral pins by writing to the port A/B control registers.
Second, configure all general-purpose 1/0 pins as input or output in the port
data direction registers. Third, select the physical interface mode of the SCCs
by writing to the SI MODE register. Fourth, program the SCC registers - the
SCON first, followed by the rest of the registers. Program the SCM with its
associated channel enable bits (ENT and ENR) last. Reset the SCCs after any
dynamic change in the parallel
1/0
ports or serial interface configuration.
MC68302 USER'S MANUAL
MOTOROLA
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