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PEB 20321
PEF 20321
Detailed Protocol Description
Data Sheet
100
2001-02-14
Receive Direction
General Features
1. The starting and ending flag (00
H
before and after a frame) as well as interframe time-
fill is recognized and extracted.
2. The number of bits within a frame is checked to be divisible by 8.
3. The number of bytes within a frame is checked to be smaller than MFL + 1.
4. A frame containing less than 8 bits may be ignored completely by the receiver.
More detailed description of the individual features:
1. a. A frame is supposed to have started if after a sequence
‘
0000 0000
’
a
‘
1
’
-bit is
recognized. The frame is supposed to have this
‘
1
’
-bit as first bit.
b. A frame is supposed to have stopped if
–
either a sequence 0000 0000 1 is found in the data stream after the frame has
started
–
or a sequence 0000 0000 is found octet synchronous (i.e. the first bit of the
sequence 00
H
is the 8 m + 1
st
bit since the starting
‘
1
’
-bit of 1.a. for an integer m).
In both cases the last bit before the sequence 00
H
is supposed to be the last bit of the
frame.
2. The check is reported in the NOB bit in the last receive descriptor of the frame.
NOB = 1: The bit length of the frame was not divisible by 8.
NOB = 0: The bit length of the frame was divisible by 8.
3. The check is reported in the LFD bit in the last receive descriptor of the frame.
LFD = 1: The number of bytes was greater than MFL.
LFD = 0: The number of bytes was smaller or equal to MFL.
Only the bytes up to the MFl + 1
st
one are transferred to the shared memory. The bytes
of the last access to the receive data section of the frame may contain erroneous bits
and shouldn
’
t be evaluated. LFD is always accompanied by NOB.
Options
There are no options in receive direction for this mode.