peb20532 Infineon Technologies Corporation, peb20532 Datasheet - Page 92

• Manufacturer Part Number: peb20532
• Description: 2 Channel Serial Optimized Communication Controller
• Manufacturer: Infineon Technologies Corporation

For receive operation SEROCCO-M monitors the incoming data stream for the Opening
Flag (7E Hex) to identify the beginning of a HDLC packet. Subsequent bytes are part of
data and are processed as normal HDLC packet including checking of CRC. Received
mapped characters are unmapped.
The abort sequence consists of the control escape character 7D
character 7E
be programmed to 7E
Octet alignment is provided through the synchronization pulses in clock mode 5b.
4.2.3
For transmit operation, SEROCCO-M inserts the HDLC header (Opening Flag), and
appends the HDLC trailer (CRC, Ending Flag), surrounding the transmit data read from
the XFIFO. Each octet (including HDLC framing flags and idle flags) is converted into
async character format (1 start, 8 data bits, 1 stop bit) and then transmitted using the
asynchronous character formatter block. Character mapping like in Octet Synchronous
PPP mode is performed.
In receive direction any async character is transferred into SEROCCO-M’s ASYNC
Character De-Formatting logic block, where it is translated back into the original
information octet. Mapped characters are unmapped and the information octets are then
transferred to the RFIFO (as in Octet Synchronous PPP mode).
4.2.4
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-M 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
Data Sheet
H
. After the control-escape, the character itself is transmitted with bit 5 inverted.
Asynchronous PPP
Data Transparency in PPP Mode
H
(not stuffed). Between two frames, the interframe time fill character should
H
H
the original character). This character is received into RFIFO and
is mapped to 7D
H
by setting bit CCR2H:ITF to ’1’.
H
character is discarded and the following character is modified
H
, 33
H
-1F
H
H
H
) are stored within the on-chip registers ACCM0..3.
, 33
is received, the 7D
H
).
92
Detailed Protocol Description
H
is discarded and the 33
H
followed by a flag
PEB 20532
PEF 20532
2000-09-14
H
is