![](http://datasheet.mmic.net.cn/330000/PEF20321_datasheet_16444041/PEF20321_83.png)
PEB 20321
PEF 20321
Detailed Protocol Description
Data Sheet
83
2001-02-14
4
Detailed Protocol Description
In the following sections, the protocol support of the MUNICH32X is described in detail
for transmit and receive direction.
Each section starts with a discussion of the general features, then proceeds with protocol
variants and options from the channel specification, and closes with a description of
interrupts and special topics.
4.1
HDLC
Transmit Direction
General Features
In transmit direction
–
the starting and ending flag (7E
H
before and after a frame)
–
the interframe time-fill between frames
–
the zero insertions (a
‘
0
’
-bit after 5 consecutive
‘
1
’
s inserted within a frame)
–
(optional) the Frame Check Sequence (FCS) at the end of a frame
is generated automatically.
Options
The different options for this mode are
–
the value of the interframe time-fill character in the channel specification:
–
7E
H
for IFTF = 0
–
FF
H
for IFTF = 1
–
the number of interframe time-fill characters programmed by FNUM in the transmit
descriptor. For the values FNUM = 0, 1, 2, the following sequences are used:
–
FNUM = 0:
frame 1, 7E
H
, frame 2 (start flag = end flag)
–
FNUM = 1:
frame 1, 7E
H
, 7E
H
, frame 2
–
FNUM = 2:
frame 1, 7E
H
, IC, 7E
H
, frame 2
–
the correction of the number of interframe time-fill characters by
1
/
8
of the number of
zero insertions by programming FA in the channel specification:
–
FA = 0:
FNUM from the transmit descriptor is taken directly to determine
the number of interframe time-fill characters as shown in
Figure 29
.
–
FA = 1:
FNUM from the transmit descriptor is reduced by
1
/
8
of the
number of the zero insertions of the frame corresponding to the
transmit descriptor as shown in
Figure 30
. This allows transmission
of long HDLC frames for a constant bit rate