DATA PROCESSING NETWORK AND IMPROVED TERMINAL

• US 3,623,013 A
• Filed: 08/13/1969
• Issued: 11/23/1971
• Est. Priority Date: 08/13/1969
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Cornelius C. Perkins, Godfrey Liu
• Inventors: Perkins, Cornelius C., Liu, Godfrey
• Primary Examiner(s): Zache, Raulfe B.
• Assistant Examiner(s): Chapuran, R. F.
• Application Number:
  US04/849,822
• Time in Patent Office: 832 Days
• Field of Search: 340/172.5
• US Class Current: 710/9
• CPC Class Codes: G06F 13/22 using successive scanning, e.g. polling G06F13/24 takes precedence
• CPC Class Codes: G06F 13/385 for adaptation of a particular data processing system to different peripheral devices
• CPC Class Codes: G06F 15/16 Combinations of two or more digital computers each having at least an arithmetic unit, a program unit and a register, e.g. for a simultaneous processing of several programs coordinating program control therefor G06F9/52; in regulating and control system G05B

Abstract

A data processing system having a central or main data processor and a plurality of remote data terminals each having at least one selectively changeable terminal address. The central processor is coupled in a poll-select environment to the various remote terminal processors via a communication link. The respective remote terminals are able to modify the poll-select sequence as set up by the central processor by selectively changing its terminal address for either the poll or select mode. Additionally, groups of the remote terminals may be assigned a selectively changeable group or broadcast address which may be changed either locally at the remote terminal or remotely by the central processor.

Claims

1. An improved addressable data terminal operatively coupled in a data communication system with a central processor through a communication net, said improved addressable data terminal comprising:

terminal address control means at each one of the data terminals including memory storage means for storing a designated terminal address data for such one terminal, said address data being in coded form and distinguishable from respective data of others of the data terminals in the system, comparator means for comparing the address portion of each received inquiry message with the terminal address stored in said terminal address control means to determine if the portion of the received message corresponds to the address data of said receiving terminal, and terminal address modifying means for selectively modifying said terminal address data so as to change the address data used by said comparator means for determining whether the address portion of a received inquiry message corresponds to the stored terminal address data.

2. The improved addressable data terminal defined in claim 1 wherein said terminal address modifying means includes expected message storage means for storing remote terminal address data in binary coded form, and means for selectively storing the modified terminal address data in place of previously stored terminal address data in said expected message storage means.

3. The improved addressable data terminal as defined in claim 1 wherein said terminal address modifying means comprises register means for storing a sequence of data bits uniquely designating the original data terminal address in a predetermined coding system, means for modifying said data bits stored in said register means for selectively altering said original data terminal address data to generate a new data terminal address data bit sequence different from the terminal data bit sequence of other terminals in said system, and means for selectively restoring said original data terminal address data bit sequence to said register means.

4. The improved data terminal as defined in claim 1 wherein said terminal is operable in a poll-select transmissiom mode and additionally including separate storage means for storing distinct terminal address data designating respectively a poll-inquiry message address and a select-inquiry message address.

5. The improved data terminal as defined in claim 4 wherein said terminal address modifying means includes means for selectively and independently modifying the address data representing the poll-inquiry message address or the select-inquiry message address respectively.

6. A system for transmitting data between a central data site and plurality of remote data terminal sites, said system comprising means at the central data site adapted to transmit a sequence of inquiry messages having an address portion and non-address portion to the remote terminal data sites, means at each remote terminal data site to temporarily store said received inquiry messages, means at each remote terminal data site to store terminal designating address data representing the remote terminal data site, means at each remote terminal data site for comparing said address portion of said received inquiry messages and with the stored terminal address data, and means for selectively modifying the terminal address data stored at at least one of said remote sites.

7. A method of transmitting data over a communication link between a central processor site and designatable ones of a plurality of addressable remote data terminals coupled via said communication link to said central processor site, said method comprising the steps of generating a sequence of inquiry messages at said central data processor site, transmitting said inquiry messages from said central processor site to said remote data terminals via said communication net in a multidrop mode, storing terminal address data at each remote terminal, said terminal address data uniquely designating the address of the remote terminal at which it is stored, temporarily storing received inquiry messages at each of said terminals receiving said inquiry message, withdrawing from storage at each remote terminal receiving an inquiry message the terminal address data designating the address of that terminal, comparing said terminal address data with an address portion of said inquiry message at each remote terminal receiving said inquiry message to determine whether such received message is addressed to the terminal receiving such inquiry message, enabling the addressed terminal to respond to said received inquiry message, and selectively changing the terminal address data stored at at least one of said remote data terminals to selectively inhibit such terminal from recognizing an inquiry message having an address portion corresponding to the original terminal address data of said terminal before said terminal address data was altered.

8. The method defined in claim 7 additionally including the steps of recognizing the failure of an addressed terminal to respond to an inquiry message addressed to it, and changing the type poll-select inquiry message whenever an addressed terminal fails to respond to an inquiry message of one type addressed to it.

9. The method of claim 7 additionally including the step of transmitting a control character from a data terminal to said central site whenever said data terminal receives an inquiry message addressed to it and its normal terminal address data has been modified.

10. The improved addressable data terminal defined in claim 1 additionally including means responsive to said comparator means for transmitting a predetermined message to the central processor.