peb20525 Infineon Technologies Corporation, peb20525 Datasheet - Page 93

• Manufacturer Part Number: peb20525
• Description: 2 Channel Serial Optimized Communication Controller For Hdlc/ppp
• Manufacturer: Infineon Technologies Corporation

4.2.3
When transporting bit-files (as opposed to text files), or compressed files, the characters
could easily represent MODEM control characters (such as CTRL-Q, CTRL-S) which the
MODEM would not pass through. SEROCCO-H maintains an Async Control Character
Map (ACCM) for characters 00-1F Hex. Whenever there is a mapped character in the
data stream, the transmitter precedes that character with a control-escape character of
7D
character e.g. 13
At the receive end, a 7D
by inverting bit 5 (e.g. if 7D
changed to 13
included in CRC calculation, even if it is not mapped.
The 32 lookup octet values (00
In addition to the ACCM, 4 user programmable characters (especially outside the range
00-1F Hex) can also be mapped using the control-escape sequence described above.
These characters are specified in registers UDAC0..3.
The receiver discards all characters which are received unmapped, but expected to be
mapped because of ACCM0..3 and UDAC0..3 register contents. If this occurs within an
HDLC frame, the unexpected characters are discarded before forwarded to the receive
CRC checking unit.
7D
The sequence of mapping control logic is:
1. 7D
2. ACCM0..3,
3. UDAC0..3.
This mechanism is applied to octet synchronous HDLC PPP mode.
Data Sheet
H
H
. After the control-escape, the character itself is transmitted with bit 5 inverted.
(control-escape) and 7E
H
and 7E
Data Transparency in PPP Mode
H
H
octets,
H
the original character). This character is received into RFIFO and
is mapped to 7D
H
character is discarded and the following character is modified
H
H
, 33
H
(flag) octets in the data stream are mapped in general.
-1F
H
H
H
) are stored within the on-chip registers ACCM0..3.
, 33
is received, the 7D
H
).
93
Detailed Protocol Description
H
is discarded and the 33
PEB 20525
PEF 20525
2000-09-14
H
is