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MC92603 Quad Gigabit Ethernet Transceiver Reference Manual
MOTOROLA
Receiver Interface Timing Modes
The frequency of IDLEs can be computed, based on the maximum frequency offset
between the transmitter and receiver in the system. The number of bytes (code groups) that
can be transmitted between a pair of IDLEs is:
(2*10
6
/N) – 1 bytes, where N is the frequency offset in ppm.
In an underrun situation, data must be repeated in order to maintain synchronization
between the clock domains. If ADIE is high and COMPAT is low, the receiver interface will
repeat a pair of IDLE bytes when underrun is imminent. This allows the user to establish
‘packets’ of data that do not contain IDLEs and the MC92603 will not insert IDLEs in the
middle of these ‘packets.’ The IDLE frequency to prevent underrun is identical to the
frequency to prevent overrun, so the same conditions apply.
If an underrun occurs, the ‘underrun’ error is reported as described in Table 3-12,
Table 3-15, or Table 3-16 for a 1-byte clock period and 2 bytes of data are repeated.
NOTE
When operating in ‘word’ mode both channels must add/delete
IDLEs simultaneously. IDLEs must appear in the data stream
for both channels simultaneously, so that IDLEs may be
repeated or deleted.
Table 3-7. Receiver Reference Clock is Slower than Transmitter Reference Clock
ADIE
COMPAT
Receive Mode
Result
Action Taken
Low
Low
—
Overrun
2 bytes of data are lost. First byte reports overrun,
second byte is skipped.
High
Low
—
Data dropped 2 consecutive IDLEs (K28.5) are dropped
High
Low
Auto-negotiate sequence
Data dropped 16 bytes dropped (/C1/C2/C1/C2/)
High
High
Idle sequence
Data dropped 2 bytes dropped (/I2/)
Table 3-8. Receiver Reference Clock is Faster than Transmitter Reference Clock
ADIE
COMPAT
Receive Mode
Result
Action Taken
Low
Low
—
Underrun
2 bytes of data are lost. First byte reports underrun,
second byte repeats byte prior to underrun.
High
Low
—
Data repeated 2 consecutive IDLEs (K28.5) are repeated
High
High
Auto-negotiate sequence
Data repeated 16 bytes repeated (/C1/C2/C1/C2/)
High
High
Idle sequence
Data repeated 2 bytes repeated (/I2/)
Summary of Contents for MC92603
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