Motorola PowerQUICC II MPC8280 Series Reference Manual page 818

CRC Calculation in Transparent Mode
24.4.2 Synchronization and the TSA
A transparent-mode SCC using the time-slot assigner can synchronize either on a
user-defined inline pattern or by inherent synchronization.
Note that when using the TSA, a newly-enabled transmitter sends from 10 to 15 frames of
idles before sending the actual transparent data due to startup requirements of the TDM.
Therefore, when loopback testing through the TDM, expect to receive several bytes of 0xFF
before the actual data.
24.4.2.1 Inline Synchronization Pattern
The receiver can be programmed to begin receiving data into the receive buffers only after
a specified data pattern arrives. To synchronize on an inline pattern:
• Set GSMR_H[SYNL].
• Program the DSR with the desired pattern.
• Clear GSMR_H[CDP].
• Set GSMR_H[CTSP, CTSS, CDS].
If GSMR_H[TXSY] is also used, the transmitter begins transmission eight clocks after the
receiver achieves synchronization.
24.4.2.2 Inherent Synchronization
Inherent synchronization assumes synchronization by default when the channel is enabled;
all data sent from the TDM to the SCC is received. To implement inherent synchronization:
• Set GSMR_H[CDP, CDS, CTSP, CTSS].
If these bits are not set, the received bit stream will be bit-shifted. The SCC loses the first
received bit because CD and CTS are treated as asynchronous signals.
24.4.3 End of Frame Detection
An end of frame cannot be detected in the transparent data stream since there is no defined
closing flag in transparent mode. Therefore, if framing is needed, the user must use the CD
line to alert the transparent controller of an end of frame.
24.5 CRC Calculation in Transparent Mode
The CRC calculations follow the ITU/IEEE standard. The CRC is calculated on the
transmitted data stream; that is, from lsb to msb for non-bit-reversed (GSMR_H[REVD] =
0) and from msb to lsb for bit-reversed (GSMR_H[REVD] = 1) transmission. The
appended CRC is sent msb to lsb. When receiving, the CRC is calculated as the incoming
24-6
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MPC8280 PowerQUICC II Family Reference Manual
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