Polling system for a duplex communications link

• US 4,251,865 A
• Filed: 12/08/1978
• Issued: 02/17/1981
• Est. Priority Date: 12/08/1978
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Bass, Robert H., Moore, Morris A.
• Primary Examiner(s): Nusbaum, Mark E.
• Application Number:
  US05/968,066
• Time in Patent Office: 802 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 179/15 AL, 179/15 BA, 340/147 R, 370/92, 370/93, 370/96, 455/38, 455/53
• US Class Current: 710/109
• CPC Class Codes: G06F 13/22 using successive scanning, e.g. polling G06F13/24 takes precedence

Abstract

Channel efficiency in a communications link between a controller and multiple portable units is increased by polling the active units and a set number of inactive units in a sequence where a "poll" consists of sending the binary coded address of the portable unit. The stream of transmitted data bits is only interrupted by a response from the portable unit, then resumed at the end of the response or a given portion of the response. During the reception of the response, certain other types of messages can be sent out by the controller. Portable responses can be automatic responses as to status, etc., or can be data initiated by the operator of the portable unit keyboard and stored in the portable unit memory until "armed" by the operator, then automatically transmitted to the controller when the portable unit address is received.

Claims

1. A method of providing more efficient use of a single communication channel of a controller/remote terminal unit link serving a multiplicity of terminal units, each unit having a permanent and unique address and comprising logic circuitry and memory, and comprising the following steps:

assigning to each said terminal unit address a permanent position in a queue of addresses stored in the memory of the controller;

the controller continuously tagging each terminal unit address in the queue as active or inactive, where "active" means that the unit is presently operating upon data or has been operating upon data within a predetermined period of time;

the controller transmitting all of the terminal unit addresses which are tagged as active units, omitting the addresses of all units tagged as inactive units, in a sequence determined by the queue of addresses;

the controller transmitting the addresses of a predetermined number of said inactive units, the choice of said units being determined by the queue of addresses;

the controller listening during said transmissions to both active and inactive units for the controller address to be received from any one terminal unit within a fixed time period following the transmission by the controller of the address of said one terminal unit, said fixed time period ending later than the beginning and earlier than the end of the next subsequent address in the transmitted sequence;

any one of the terminal units responding to said respective assigned address by transmitting the controller address followed by a data message;

the controller recognizing that reception of the controller address during said fixed time period is a response from that terminal unit having the address immediately preceding the address being transmitted at the time of controller address detection;

upon such reception, the controller interrupting the sequence of said address transmissions, storing the received predetermined message and any immediately subsequent data from the responding terminal unit;

the controller processing said predetermined message; and

the controller resuming transmission of the sequence of messages, beginning with the address which was previously interrupted.

2. The method in accordance with claim 1 wherein said addresses are binary coded addresses.

3. The method in accordance with claim 2 wherein each said binary coded address consists of at least two digital words, and one of said words is unique in the system.

4. The method in accordance with claim 1 wherein the transmission and reception of addresses and responses is done via an RF link.

5. The method in accordance with claim 1 and further including the step of retransmitting by the controller, on a second transmission link, of at least some of the received responses from terminal units.

6. The method in accordance with claim 1 and further including the step of inserting non-data signals between each succeeding pair of addresses in each sequence.

7. The method in accordance with claim 1 wherein the step of processing the received predetermined message includes the steps of:

checking said message for completeness and accuracy; and

checking to see if the number of incomplete messages sequentially received from one terminal unit exceeds a predetermined number.

8. The method in accordance with claim 7 and including, if said number of received incomplete messages exceeds said predetermined number, the controller erasing the message and tagging the transmitting portable unit as inactive.

9. The method in accordance with claim 7 and including, if said number of received messages does not exceed said predetermined number, the controller storing the messages and the controller retransmitting the messages on a second transmission link.