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When there are not enough buffers, frames may be accepted if the appropriate bit is set in the
receive frame status error mask (see 4.1.1.2 RECEIVE STATUS WORD for a description) in the
initialization table.
2.2.13.8 NUMBER OF OVERRUNS. This statistic represents the nu mber of times the TBe detected
II
a FIFO overrun during receive. Frames may be stored into memory up to the overrun error if the
appropriate bit is set in the receive frame status error mask (see 4.1.1.2 RECEIVE STATUS WORD
for a description) in the initialization table.
2.2.14 Modem Error Counters
The following three counters are the number of noise bursts detected that occurred when noise
was not expected. Noise may be expected in some procedures in the protocol due to collisions.
These counters do not track such noise bursts, but only noise bursts that are due to errors or
unexpected noise on the medium.
2.2.14.1 NON-SILENCE. Non-silence is the number of received periods of non-silence.
2.2.14.2 FCS ERRORS. FCS errors track the number of received frames with FCS (or CRC) errors
and the E-bit reset.
2.2.14.3 E-BIT ERRORS. E-bit errors count the number of received frames with the E bit set in the
end delimiter. The E bit, or error bit, is set by the regenerative repeater (headend remodulator),
when the headend detects a FCS error on the forward channel. If this error occurs, frames may
be accepted if the appropriate bit is set in the receive frame status error mask (see 4.1.1.2 RECEIVE
STATUS WORD for a description) in the initialization table.
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2.2.14.4 FRAME FRAGMENTS. This counter represents the number of frame fragments (start
delimiter (SO) not followed by a valid end delimiter (EO)). A valid frame consists of only data
(zero or one MAC symbols) between the SO and the EO. If an SO is detected and then, before a
valid ED, the TBC detects either silence, non data (not part of the aligned ED), or bad signal, then
this counter is incremented. Note that this includes abort sequences.
2.2.15 DMA Dump Area
The OMA dump area contains the pointers and function codes of the four DMA channels when
a bus/address error occurs (see 2.2.11 Interrupt Status Words). The dump area can be used to
check all of the pointers and to see if one of them is out of sequence. This should be the pointer
that caused the bus/address error.
MC68824 USER'S MANUAL
MOTOROLA
2-21
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