Motorola MSC8101 ADS User's Guide Page 44

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1-20 MSC8101 User’s Guide
MSC8101 Overview
Figure 1-5. Example SCC UART RxBD Processing
1.3.7.7 TxBD Processing Example
Figure 1-6 shows how the TxBD is processed in SCC UART mode. When the CP detects
that the TxBD.bd_cstat.R (ready) is set, it starts transmitting the buffer. After the
buffer is transmitted, the CP waits for the next descriptor’s TxBD.bd_cstat.R to be set
before proceeding. When the CP detects that a descriptor’s TxBD.bd_cstat.W (wrap)
is set, indicating that this BD is last in the BD table, it returns to the start of the BD table
after this last BD is processed. The CP clears TxBD.bd_cstat.R (not ready) after
using a TxBD, which keeps it from being retransmitted before the SC140 core confirms it.
However, some protocols support a continuous mode for which TxBD.bd_cstat.R
remains set after the buffer is closed to allow the buffer to be resent next time the CP
accesses this BD. Continuous mode is enabled by setting TxBD.bd_cstat.CM.
8000
xxxx
0001
2020
8000
xxxx
0055
4750
8000
xxxx
FF07
F000
A000
xxxx
0089
C000
RxBD 1
RxBD 2
RxBD 3
RxBD n
RxBD Table
CPM Action:
RxBD 2
1. Receives characters and stores them in the buffer at 0x554750.
RxBD 1
1. Receives characters and stores them in the buffer at 0x12020.
2. Clears RxBD.bd_cstat.E after buffer is full (8 bytes received).
3. Writes 0x08 to RxBD.bd_length.
1. Receives characters and stores them in the buffer at 0x89C000.
2. Clears RxBD.bd_cstat.E after buffer is full.
3. Proceeds to RxBD 1 since RxBD.bd_cstat.W=1.
RxBD 3
1. Receives characters and stores them in the buffer at 0xFF07F000.
E W I C A CM ID AM CD
012 3 4 5 678 9
10 11 12 13 14 15
SCC UART RxBD.bd_cstat
4. Proceeds to next RxBD since RxBD.bd_cstat.W=0.
BR FR PR OV
4. Proceeds to the next RxBD since RxBD.bd_cstat.W=0.
Byte 1
Byte 2
Byte 8
...
MRBLR=8 bytes
Byte 1
Byte 2
Empty
Byte 1
Byte 4
Empty
...
4. Proceeds to next RxBD since RxBD.bd_cstat.W=0.
Idle
time-out
occurred
Byte 4 has
framing
error
2. Sets RxBD.bd_cstat.ID because a programmable number
of consecutive idle sequences (MAX_IDL) was received.
3. Writes 0x02 to RxBD.bd_length. (Two bytes received before
Error
2. Sets RxBD.bd_cstat.FR because byte 4 contains a frame
error.
3. Writes 0x04 to RxBD.bd_length.
idle time-out occurred).
Byte 1
Byte 2
Byte 8
...
2. Clears RxBD.bd_cstat.E after buffer is full (8 bytes received).
RxBD
x
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