MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
H-1
Appendix H
Serial ATM Scrambling, Reception, and SI Programming
H.1
ATM Cell Payload Scrambling
The ATM controller provides a scrambling option on a per line basis for cell payload bytes using the
polynomial X
43
+1.
Figure H-1
shows the payload transmitter and receiver scrambling mechanism.
Figure H-1. ATM Cell Payload Scrambling Mechanism
The context of the transmit and receive scrambling mechanism is independent of the cell’s virtual
connection. The seed value for the scrambling algorithm for a particular cell is obtained from the 43 cell
payload bits transmitted or received immediately prior to the current cell. Even though two consecutive
cells may be from different connections, the scrambling mechanism ignores this.
H.2
Receiving Serial ATM Cells
Figure H-2
shows the serial ATM receive procedure. After start-up when MRBLR is zero, the HEC
delineation procedure begins (see below). Once complete, cell reception commences.
For each cell received, the HEC is checked. If the HEC is incorrect, the cell is still received unless the
receiver loses cell delineation. If the cell is an empty cell, the payload is discarded. If there is a header
match using the lookup table then the cell payload is received. When the external CAM option is enabled,
the cell is received before the CAM match is checked.
Operation continues in this manner until the
RESTART
RECEIVE
(ATM Opcode = 101) command or a FIFO
overrun error occurs or the user disables the SCC receiver. Received cells may have their payloads
descrambled as described earlier.
43-Bit Delay
Transmit Data
Scrambled Data
Receive Data
43-Bit Delay
Transmitter
Receiver
Descrambled Data
Summary of Contents for PowerQUICC MPC870
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Page 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Page 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
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Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Page 1336: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 16 Freescale Semiconductor ...
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Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...