Communication network with time coordinated station activity by time slot and periodic interval number

• US 5,537,549 A
• Filed: 04/28/1993
• Issued: 07/16/1996
• Est. Priority Date: 04/28/1993
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Siorek, Timothy, Engdahl, Jonathan R., Lucak, Mark A., Gee, David J.
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): DINH, DUNG C
• Application Number:
  US08/054,323
• Time in Patent Office: 1,175 Days
• Field of Search: 370/85.1, 370/92, 370/95.3, 370/100.1, 370/105.1, 395/200.06, 395/200.19, 395/865, 395/200.2, 395/730
• US Class Current: 709/224
• CPC Class Codes: G05B 19/0421 Multiprocessor system
• CPC Class Codes: H04L 12/40026 Details regarding a bus guardian
• CPC Class Codes: H04L 12/40032 Details regarding a bus interface enhancer
• CPC Class Codes: H04L 12/4035 in which slots of a TDMA packet structure are assigned based on a contention resolution carried out at a master unit TDM/TDMA multiplex systems per se H04J3/1694; hybrid switching systems H04L12/64
• CPC Class Codes: H04L 12/407 with decentralised control
• CPC Class Codes: H04L 12/417 with deterministic access, e.g. token passing
• CPC Class Codes: H04L 2012/4026 Bus for use in automation systems

Abstract

Activity on a digital communication network is divided into periodic intervals and during a segment of each periodic interval a moderator station broadcasts a numerical count of the periodic intervals to all stations on the network. Each station has a memory in which a numerical value is stored, and a comparator that compares the numerical value to the numerical count received from the network. When the numerical count of the periodic intervals equals the numerical value, an apparatus within the station performs a defined operation, such as transmitting a message over the network or synchronizing a clock in the station to a master time standard. The equality of the periodic interval count and the numerical value also can be used to determine when to signal an external device. By using the count of the periodic intervals in this manner, the operation of several stations on the network can be coordinated.

Claims

1. A communication network comprising:

a medium through which messages can be transmitted by a plurality of stations during each one of a plurality of periodic intervals, in which the periodic intervals are numbered consecutively according to a predetermined modulus, and in which each periodic interval has a fixed, predetermined duration and includes a set of time slots during which stations are afforded an opportunity to transmit, wherein each time slot is identified by an associated slot number, with the slot number being included in the transmission made during each time slot to thereby identify the current time slot;

a first station which is connected to said medium, and which at a fixed, predetermined point during each periodic interval, transmits through said medium a moderator message which includes a periodic interval number in addition to the slot number, in which the periodic interval number represents a current value for the consecutive numbering of the periodic intervals; and

a second station including a receiver coupled to said medium to receive transmissions made by other stations, the second station including;

a memory for storing a predefined value corresponding to one or more periodic interval numbers of interest;

a comparator connected to the receiver and the memory for comparing the periodic interval number from a received moderator message to the predefined value; and

means connected to the comparator for performing a defined operation when the periodic interval number from a received moderator message equals the predefined value.

2. The communication network as recited in claim 1 wherein said second station receives from the medium a control message containing the predefined value;

and said second station further includes a means for loading the predefined value from the control message into the memory.

3. The communication network as recited in claim 2 wherein the control message also contains a future time value;

said second station further includes a clock which provides a numerical time signal; and

wherein the means for performing a defined operation alters the clock if the numerical time signal does not substantially equal the future time value at a fixed point in time after the comparator indicates receipt of a moderator message in which the periodic interval number equals the predetermined value.

4. The communication network as recited in claim 1 wherein said second station further includes a transmitter connected to send messages through said medium;

and wherein the means for performing a defined operation enables said transmitter to transmit a message when both (a) the current time slot is equal to a slot number allocated for transmission by the second station, and (b) the periodic interval number from the most recently received moderator message equals the predetermined value.

5. The communication network as recited in claim 1 wherein said memory also stores a data mask;

and said comparator logically combines the data mask, the periodic interval number and the predefined value to determine when to perform the defined operation.

6. A media access controller for a communication network in which activity on the communication network is divided into a succession of periodic intervals which are numbered consecutively according to a predetermined modulus, and in which each periodic interval has a fixed, predetermined duration and includes a set of time slots during which each one of a plurality of stations are sequentially afforded an opportunity to transmit, wherein each time slot is identified by an associated slot number, with the slot number being included in the transmission made during each time slot to thereby identify the current time slot, and during each periodic interval a network moderator station transmits a moderator message containing a periodic interval number in addition to the slot number, in which the periodic interval number represents a current value for the consecutive numbering of the periodic intervals, said media access controller comprising:

an interface for connecting to an external data processing device to exchange data therebetween;

a receiver connected to the communication network to receive messages therefrom;

a first register connected to said receiver for storing the periodic interval number obtained from each successively received moderator message;

a memory for storing an outgoing data packet received from the external processing device, and a specified count corresponding to a future periodic interval during which the outgoing data packet is to be transmitted;

a transmitter connected to said interface and to said memory for sending the data message over the communication network; and

an access control circuit which is connected to said transmitter, the first register and the memory, and which enables said transmitter to send data over the communication network when the periodic interval number in the first register equals the specified count for transmitting the outgoing data message.

7. The media access controller as recited in claim 6 wherein said specified count is contained in a start-of-periodic-interval pseudo packet which is also received from the external processing device.

8. The media access controller as recited in claim 7 wherein said memory comprises a first in, first out memory.

9. The media access controller as recited in claim 6 further comprising a second register for storing a data mask;

and wherein said access control circuit logically combines the data mask, the periodic interval number from the first register and the specified count for transmitting the outgoing data message from the memory to determine when to enable said transmitter.

10. A station for a digital communication network in which activity on the digital communication network is divided into a series of periodic intervals in which the periodic intervals are numbered consecutively according to a predetermined modulus, and in which each periodic interval has a fixed, predetermined duration and includes a set of time slots identified by an associated slot number, with the slot number being included in the transmission made during each time slot to thereby identify the current time slot, said station comprising:

a modem connected to the digital communication network;

a transmitter connected to said modem to send messages over the digital communication network;

a first mechanism, coupled to said modem, for detecting a moderator message sent over the digital communication network by a moderator station during a fixed, predetermined point of each periodic interval, wherein the moderator message includes a periodic interval number in addition to the slot number, in which the periodic interval number represents a current value for the consecutive numbering of the periodic intervals; and

a second mechanism responsive to said first mechanism for controlling said transmitter to delay transmission of an outgoing message by suppressing transmission during the time slot allotted to the station when the periodic interval number is less than a predefined value, and by enabling transmission during the next time slot allotted to the station after the periodic interval number has reached the predefined value.