CD2401 Intel, CD2401 Datasheet - Page 83

• Manufacturer Part Number: CD2401
• Description: Multi-protocol Communications Controller
• Manufacturer: Intel

6.4
6.4.1
Datasheet
Table 17. Description of States
Number
0
1
2
3
4
5
6
7
Note: When returning to the SYN Hunt state, RxITB is cleared.
Key:
Hunt
i
c
0
1
NOTES:
X.21 Call Setup Mode
The X.21 call setup protocol uses a combination of synchronous data and control leads to control
call progress, between a DCE and a DTE. The data can be steady-state conditions (all ‘1’s, all ‘0’s,
alternating ‘1’s and ‘0’s) or character synchronous data. The control leads are used in conjunction
with the steady-state-data conditions to pass change-of-state information between the DCE and
DTE. To enable detection of steady-state conditions, the SSDE bit (COR3[4]) must be set.
X.21 Transmit
To minimize CPU intervention in the transmit direction, a modified version of the ETC is used.
ETC mode is controlled through COR2. When enabled, ETC mode provides a means of
transmitting steady state or repetitive data patterns synchronized to the control lead. The ETC
consists of a sequence of four bytes passed to the CD2401 as normal transmit data, in the format
shown in
1. The SYN Hunt state not shown. The SYN Hunt state consists of two substates that look for a received
BGETHDR
BESCF
BESCL
BGETXT
BBCC
BBCC2
BWEOT
BXP
2. Conditions for the state table:
SYN-SYN pattern. Upon receiving SYN-SYN, the state moves to BGETHDR.
CRC-16 enabled
EBCDIC character set
Name
= Go to SYN Hunt state
= initialize BCC
= calculate CRC
= clear state flag, for example 0-RxITB clears the RxITB flag
= set state flag
Table
18.
SYN-SYN received, looking for next non-SYN character.
The first DLE after opening SYNs received.
Received DLE, not the first for this frame.
The first non-SYN character after opening SYNs received. The first character is either:
STX, SOH, ETX (if RxITB = 1), or ETB (if RxITB = 1).
A proper end-of-text received, the channel is ready for the first BCC character. Proper
protocol: ETX, ETB, or ITB in non-transparent mode; DLE-ETX, DLE-ETB, or DLE-ITB in
transparent mode.
Received the first BCC character, CD2401 is ready for the second BCC character.
Continue receiving in this state until a PAD character is detected.
Transparent receive: look for escape DLE, else keep receiving.
Multi-Protocol Communications Controller — CD2401
Description
83