Browse Prior Art Database

Determination of Asynchronous Line Parameters and Device Class Via Software

IP.com Disclosure Number: IPCOM000121443D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 4 page(s) / 162K

Publishing Venue

IBM

Related People

Manulik, RJ: AUTHOR [+2]

Abstract

A software method for determining asynchronous line parameters and device class is disclosed. The device classes for this method are NPTs (Non Programmable ASCII Terminals), and PWSs (Programmable Work Stations running SNA-A). The method consists of loading software on the system that must do the determination, and having each class of device send out a unique initial sequence (a Null XID for a PWS and a key sequence (..CR) for a NPT). Limiting the range of line parameters used is necessary so that the class of device and line parameters used can be determined, and the communication hardware set accordingly.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 49% of the total text.

Determination of Asynchronous Line Parameters and Device Class Via
Software

      A software method for determining asynchronous line
parameters and device class is disclosed.  The device classes for
this method are NPTs (Non Programmable ASCII Terminals), and PWSs
(Programmable Work Stations running SNA-A).  The method consists of
loading software on the system that must do the determination, and
having each class of device send out a unique initial sequence (a
Null XID for a PWS and a key sequence (..CR) for a NPT).  Limiting
the range of line parameters used is necessary so that the class of
device and line parameters used can be determined, and the
communication hardware set accordingly.

      In this implementation, a Finite State Machine (FSM) is used as
the program structure.  The FSM receives character bytes from the
hardware and acts on them accordingly.  Once the FSM has received a
valid initial sequence, it sets the hardware and may notify another
module of the device class. If an invalid device is connected, or an
invalid initial sequence is received, the FSM will reset itself to
allow another device to connect.  A timer is also included in this
implementation where if the FSM cannot detect the device class or
line parameters after a certain time period, it will reset.  This
method of line parameter determination has two advantages: it can run
on hardware that has not been explicitly designed for this type of
determination, and it is more flexible than hardware implementations.
The hardware that this may run on is standard asynchronous receive
hardware found on most all asynchronous devices. The only requirement
is that the hardware must be able to change its receive baud rate and
parity between receiving bytes.  The program uses the bytes that are
parsed out of the incoming data stream to make its determination of
the line parameters.  Since this is a software-based package, certain
values (invalid character reset, range of baud rates, etc.) can be
easily changed according to the system needs.

      The operation of the program is to set its hardware at a
specific value, and then analyze the characters received. The
determination of the characters that should be received on an
error-free line is done by taking into account the data sent and the
degree of mismatch in the baud rates. Asynchronous hardware
recognizes a character as a drop in the line (start bit), any 8 bits,
and an ending high signal (stop bit).  An example of character
determination is given in Fig. 1.

      Fig. 1 is the signal for the first character sent in the
initial sequence if the attached device is a NPT ('2E'X, a period).

      If the the attached device has a baudrate that is one-fourth of
the program hardware setting, the program will receive 4 bits for
every bit that was sent out by the attached device and will then see
the following bit stream:
           ssss 0000 1111 1111 1111 0000 1111 0000 pppp ssss
  ...