DATA TRANSMISSION METHOD AND SERIAL LOOP DATA TRANSMISSION SYSTEM

• US 3,633,166 A
• Filed: 05/05/1970
• Issued: 01/04/1972
• Est. Priority Date: 05/16/1969
• Status: Expired due to Term

• Current Assignee: Jean L. Picard
• Original Assignee: Jean L. Picard
• Inventors: Picard, Jean L.
• Primary Examiner(s): Pitts, Harold I.
• Application Number:
  US05/034,781
• Time in Patent Office: 609 Days
• Field of Search: 340/163
• US Class Current: 370/395.1
• CPC Class Codes: H04L 12/423 with centralised control, e.g. polling

Abstract

A method and system for transmitting data between a central control unit and a plurality of terminals arranged in a loop configuration in which each terminal includes a shift register and a two-position switch, the former short circuiting the terminal and the latter interposing the shift register in the loop. When the central unit wants to know which terminals have data to transmit to it, it sends a B character on the loop, which is intercepted by the registers of all the terminals. The terminals which have data to transmit place their switch in its second position and load their register with their identification number. The central unit then sends a sequence of A characters which are intercepted by the terminals which have their switch in the second position and which shift the identification numbers from register to register and so forth to the central unit, thus enabling the central unit to determine which terminals have data to transmit.

Claims

1. A method for establishing communications between a central station and a plurality of remote stations connected in a serial loop with said central station comprising the steps of:

transmitting from said central station, characters having a first predetermined bit configuration followed by at least one character of a second predetermined bit configuration and immediately followed by characters having said first predetermined bit configuration;

at each said remote station monitoring the bit configurations on the loop for detecting the presence of said second predetermined bit configuration;

inserting a unique bit configuration identifying the remote station following the detection of said second predetermined bit configuration when the station has data to send to the central;

buffering a predetermined number of incoming bits from the loop before passing the buffered bits onto the next remote station on the loop;

monitoring the buffered bits to detect the said first predetermined bit configuration; and

passing the received bit stream directly onto the next remote station in the loop when the said first predetermined bit configuration is detected amongst the buffered bits whereby said central station receives from the lAst station in the loop a plurality of unique bit configurations, each identifying one remote station which has data to send to the central and requires service which may be initiated by the central in any order which is appropriate since the central is advised of all remote stations requiring service.

2. A method for establishing communications between a central station and a plurality of remote stations connected in a serial loop with said central station comprising the steps of:

transmitting from said central station characters having a first predetermined bit configuration followed by at least one character of a second predetermined bit configuration and immediately followed by characters having said first predetermined bit configuration;

at each said remote station;

monitoring the bit configurations on the loop for detecting the second predetermined bit configuration, inserting a unique bit configuration identifying the remote station following detection of the said second predetermined bit configuration when the remote station has data to send to the central station, following detection of the said second predetermined bit configuration buffering a predetermined number of incoming bits from the loop before passing the buffered bits onto the next remote station on the loop, monitoring the buffered bits to detect the said first predetermined bit configuration, and passing the received bit stream directly onto the next remote station in the loop when the said first predetermined bit configuration is detected whereby the said central station receives from the last remote station in the loop a plurality of unique bit configurations each identifying one remote station which has data to send to the central in the inverse order of their physical arrangement on the loop preceded by the said second predetermined bit configuration and followed by said first predetermined bit configuration, and at said central station after receipt of said unique address followed by said first predetermined bit configuration transmitting a third predetermined bit configuration followed by a unique remote station address from amongst the unique station addresses received for enabling the addressed remote station to send data via the loop to the central station and repeating the sequence until all stations needing service have transmitted data to the central station.

3. A communications system for providing data transmission between a central station and a plurality of remote stations connected in a serial loop with said central station comprising:

means at said central station for transmitting characters having a first bit configuration followed by at least one character having a second bit configuration and immediately followed by characters having said first bit configuration;

input means at each remote station for receiving data bits from the preceding station;

output means at each remote station for transmitting data bits to the next succeeding station;

shift register means at each remote station connected to the input means for registering a predetermined number of consecutive bits;

switch means for alternatively connecting the shift register to the output means in one state and the input means directly to the output means in its other state;

decoder means responsive to the contents of said shift register for detecting the said first and second bit configuration and providing outputs indicative thereof; and

control means responsive to the output indicative of the detection of the second bit configuration for causing said switch means to assume its said other state and for inserting a unique station identification code in the said shift register over the previously received said second bit configuration and for causing said switch means to assume its said first state when the output from the decoder means indicates the reception of the said first bit configuration whereby said central station receives from The output means of the last remote station on the loop a plurality of unique bit configurations each identifying one remote station which has data to send to the central and requires service which may be initiated by the central in any appropriate order since the central is advised of all the remote stations requiring service.

4. A communications system as set forth in claim 3 in which the first and second bit configurations and said unique station identification codes all have the same number of bits.

5. A method for establishing communications between a central station and a plurality of remote stations connected in a serial loop with said central station comprising the steps of:

transmitting from said central station characters having a first predetermined bit configuration followed by at least one character having a second predetermined bit configuration immediately followed by characters having said first predetermined bit configuration;

at each said remote station buffering a predetermined number of incoming bits from the loop before passing the buffered bits onto the next station on the loop;

monitoring the buffered bits for detecting the presence of said first bit configuration following the second bit configuration; and

inserting a unique bit configuration identifying the remote station when the station has data to send to the central station in place of the said first bit configuration which follows the said second bit configuration whereby the central station receives from the last remote station in the loop a plurality of unique bit configurations each identifying one remote station which has data to send to the central station and requires service which may be initiated by the central in any order which is appropriate since the central is advised of all remote stations requiring service.