Browse Prior Art Database

Support of X.21 on an RS422 Design

IP.com Disclosure Number: IPCOM000115240D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 6 page(s) / 109K

Publishing Venue

IBM

Related People

Benayoun, A: AUTHOR [+3]

Abstract

Disclosed is a method showing that a data communication adapter providing a U.S. high-speed electrical interface RS422 cannot be connected to EMEA X.21 public data communication networks. The advantages of the current solution are the following: o One adapter to be developed to support either RS422 or X.21 o The choice of the interface RS422 or X.21 is programmable o Only one P/N to be supported

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Support of X.21 on an RS422 Design

      Disclosed is a method showing that a data communication adapter
providing a

U.S.

  high-speed electrical interface RS422 cannot be
connected to EMEA X.21 public data communication networks.  The
advantages of the current solution are the following:
  o  One adapter to be developed to support either RS422 or X.21
  o  The choice of the interface RS422 or X.21 is programmable
  o  Only one P/N to be supported

Applications of the invention:
  o   Any high speed data communication adapter to be designed to
       operate both in the U.S. and in EMEA
  o  Attachment to either Switched X.21 networks or Leased X.21
       networks

Hardware Description of the Invention - The RS422 and the X.21 high
speed interfaces provide the following common points:
  1.  Signal set:
      RS422 Signal Set          X.21 Signal Set        I/O
   RTS .... Request to Send   Control ......... C     Output
   TD ..... Transmit Data     Transmit Data ... T     Output
   RD ..... Receive Data      Receive Data .... R     Input
   CTS .... Clear to Send     Indicate ........ I     Input
   RCLK ... Receive Clock     Receive Clock ... S     Input
   TCLK ... Transmit Clock           N/A              Input
        Figure 1.  RS422 and X.21 Signal Set
  2.  The electrical interface is made of V.11 drivers and receivers

The difference between the RS422 interface and the X.21 interface is
protocol oriented.  The CCITT specifies for the X.21 interface the
detection of three states:
  1.  All ONEs on RECEIVE DATA during 16 RECEIVE CLOCK pulses and
       INDICATE in the OFF state
  2.  All ZEROs on RECEIVE DATA during 16 RECEIVE CLOCK pulses and
       INDICATE in the OFF state
  3.  Alternating ZEROs and ONEs on RECEIVE DATA during 16 RECEIVE
       CLOCK pulses (that is 010101...) and INDICATE in the OFF state

The idea is to implement this state detection in the design of the
RS422 interface.  Fig. 2 is a block diagram which shows such an
implementation.

The control logic is described in Examples A & B.

Software Description of the Invention - At power-on the design is
con...