CD2231

Manufacturer Part NumberCD2231
DescriptionCD2231 Intelligent Two-channel Lan And Wan Communications Controller
ManufacturerIntel Corporation
CD2231 datasheet
 


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CD2231 — Intelligent Two-Channel LAN and WAN Communications Controller
6.4.1
Framing
An MNP4 (V.42) frame consists of a start flag, data octets, a stop flag, and a 16-bit FCS (frame
check sequence). The FCS uses the polynomial (
and inverted. The character format uses asynchronous framing with 8 data bits, no parity, and one
Stop bit. In-band flow control (XON/XOFF) is not permitted in this mode.
The start flag is a three octet sequence consisting of the start character, escape character, and STX
(0x02). The stop flag is a two octet sequence consisting of the escape character and ETX (0x03).
During transmit, if an escape character is encountered in the data stream, it is duplicated.
Conversely, the receiver discards the second of two sequential escape characters.
MNP4 is the data-link layer of ARAP 1.0 (AppleTalk Remote Access Protocol). ARAP 2.0 is the
same as MNP4 except for the two start and escape characters.
The CD2231 uses two Special Character registers (SCHR1 and SCHR2) to hold the definition of
the start and escape characters. There is no mode selection within the CD2231 that allows it to
determine whether it is in an ARAP 1.0 or ARAP 2.0 environment. It builds and detects frames
using the values in the two Special Character registers. The user must load the two Special
Character registers with the appropriate start and escape characters for the version in use during
channel initialization. The two special characters for each protocol are shown in
Table 12. Special Character Definition
Special Character
Register 1 and 2
SCHR1 contains the start
character
SCHR2 contains the escape
character
For both versions of ARAP, frames begin with SCHR1, SCHR2, STX, and end with SCHR2 and
ETX:
ARAP 1.0— SYN, DLE, STX, data, data, data, ... DLE, ETX
ARAP 2.0— SOH, ESC, STX, data, data, data, ... ESC, ETX
Both versions escape the escape character (in SHCR2) by duplicating it if it appears within the data
stream.
6.4.2
MNP 4/ARAP FCS (Frame Check Sequence) Calculation
Both versions use the (
with remainder equal to 0x1D0F. The frame body and ETX octet of the stop flag are included in the
FCS calculation for both versions. The start flag and all DLE (ARAP 1.0)/ESC (ARAP 2.0) octets
that are used for transparency are excluded from the FCS calculation.
illustrate the characters used in the FCS calculation. Data used in FCS calculation is in bold print.
Figure 17. ARAP 1.0 Frame
Start Flag
SYN
DLE
STX
data
74
16
12
x
+
x
ARAP 1.0
ARAP 2.0
SYN
SOH
DLE
ESC
16
12
5
) polynomial, preset to all ‘1’s, transmitted and inverted
x
+
x
+
x
+
1
T
data
DLE
DLE
data
5
), preset to all ‘1’s, transmitted,
+
x
+
1
Table
12.
Figure 17
and
Figure 18
End Flag
data
DLE
ETX
FCS1
FCS2
Datasheet