Motorola MPC860 PowerQUICC User Manual page 716

Part V. The Communications Processor Module
XOR_NEXT=1
End of Frame
26.6 Exceptions to RFC 1549
¥ An unmapped control character that follows 0x7D is modiÞed by the XOR process.
The CRC check should catch this.
¥ In addition to the abort sequence, frames are terminated by the following errors:
Ñ CD (carrier detect) lost
Ñ Receiver overrun
Ñ Framing error
Ñ Break sequence
¥ If an invalid sequence(0x7D7D) is received, the Þrst control escape character is
discarded, and the second is unconditionally XORed with 0x20. The sequence is
thus stored in the buffer as 0x5D.
26-4
Rx CHAR
CHAR < 0x20
?
False
XOR_NEXT
?
False
True
CHAR=CTRL ESC
?
False
True
CHAR=Closing Flag
?
False
Write CHAR to
Buffer
Exit
Figure 26-2. Receive Flowchart
MPC860 PowerQUICC UserÕs Manual
True
True
True
CHAR=Closing Flag
?
False
CHAR Å 0x20
XOR_NEXT=0
Abort
True
Mapped
?
False
Exit
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