Panasonic UF-E1 Service Manual page 164

UF-E1
0001
0003 - 001F
007D
00CF
00FF
8001 - 801F
807D
80CF
80FF
b. Frame processing
Frames are processed with byte as a unit in byte synchronous and asynchronous processing (byte-
stuffing).
Also, in asynchronous processing, in order to transmit transmission control codes (00h - 1Fh) trans-
missively, Asynch Control Character Map (ACCM) must be sued. For the control escape code, 7Dh
is used instead of normal ESC (Escape 1Bh) and the control code is transmitted in 2 bytes in control
escape code, as shown in Figure 6.5.2.3. When transmitting, escape is set after FCS calculation
and, when receiving, escape is taken off after FCS calculation.
In bit-synch processing, the Shared-Zero Mode stipulated in HDLC is not used in PPP. (In Shared-
Zero Mode, 0 on the 8th and first bit of the continuous idle sequence is shared.)
Frames shorter than 4-byte length (when using 2-byte FCS) and 6-byte length (when using 4-byte
FCS), frames ending with escape character and ending flag, and frames with bit-overflow are dis-
carded as ineffective frames and not as FCS errors.
When this is done, general processing used in HDLC are used in the same manner. Example of this
is zero-insert and zero-delete, which means "0" is always inserted after five continuous "1" bit
frames when transmitting and "0" after five continuous "1" bit frames is ignored when receiving.
Key Point
1
1 Control-Escape code is 7Dh.
2 Flag 7Eh and control 03h are escaped.
3 When transmitting, after FCS calculation, all bytes are checked. Flag/ Control-Escape/ACCM bytes are
replaced by 2-byte escape sequence(7Dh/NNh
7Dh/NNh [NNh = (Original byte) <XOR
[Example] 7Eh
7Dh
03h
11h
13h
91h
93h
4 When receiving, before FCS calculation, those smaller than 2 ch bytes and those of ACCM flag will be
omitted from subjects. Control-Escape code (7Ch) is also omitted. 2Ch XOR next. Lastly, calculate FCS.
Note 1: 7Ch/NNh mean 2 bytes of 7Ch and NNh.
Note 2: XOR means Exclusive OR.
Table 6.5.2.3 Special protocol values of PPP frames (RFC 1681)
Number
Bad protocol (self description bad option: Type 10)
Reserved (Increased efficiency in transmissivity process-
ing (When non-synchronous escape control is used)
Reserved (Non-synchronous escape code)
Reserved (PPP NLPID)
Reserved (Increased efficiency in compression process-
ing (When both ACFC and PFC are used)
Not used
Not used
Not used
Not used
Control-Escape code is 7Dh
7Dh/5Eh (Flag)
7Dh/5Dh (Control-Escape)
7Dh/23h (ETX)
7Dh/31h (XON/DC1)
7Dh/33h (XOFF/DC3)
7Dh/B1h (XON = DC1 + Parity)
7Dh/B3h (XOFF = DC3 + Parity)
Figure 6.5.2.3 Processing of an asynchronous formula control code
Use
2
Control code is sent in 2 bytes with escape added and 2ch XOR
(Note 1)
). The second byte is obtained by the following calculation.
(Note 2)
> (20h)]
160