Network interface apparatus and method for reducing conflicts through the use of times

• US 5,378,067 A
• Filed: 09/24/1993
• Issued: 01/03/1995
• Est. Priority Date: 02/07/1991
• Status: Expired due to Fees

• Current Assignee: Datacard Corp. (Entrust Corp.)
• Original Assignee: Datacard Corp. (Entrust Corp.)
• Inventors: Hardy, John D. Jr., Severson, Verne L.
• Primary Examiner(s): Bowler, Alyssa H.
• Assistant Examiner(s): HARRITY, JOHN E
• Application Number:
  US08/126,682
• Time in Patent Office: 466 Days
• Field of Search: 395/800, 395/325
• US Class Current: 709/237
• CPC Class Codes: G06F 13/387 for adaptation of different data processing systems to different peripheral devices, e.g. protocol converters for incompatible systems, open system
• CPC Class Codes: H04L 12/40032 Details regarding a bus interface enhancer

Abstract

A network interface circuit is interconnected to a network terminal to enable the network terminal to communicate with other network terminals on a local terminal network. The network interface circuit includes an RS-485 transceiver including a driver and transmitter function. A status timer 42 controls a status line back to the network so as to indicate to the network terminal when the network is in use. A driver timer is present to automatically enable the driver function of the RS-485 circuit when a start bit is received from the network terminal, the driver timer being designed to insure that RS-485 transmitter function remains active until all the data has been transmitted.

Claims

1. In a communications network for transmitting data on a communication medium coupling a plurality of terminal processors, a network interface circuit associated with each terminal processor comprising:

a transceiver for interfacing said terminal processor to said network, said transceiver including a driver for driving data on said communication medium, said driver continuing to drive the communication medium for a period of time, t(DRIVER HOLD), beyond the time data is transmitted;

status means for providing status information to said terminal processor indicating whether data is being transmitted on said communication medium, said status means further comprising a status line coupled to said terminal processors, wherein said status line is made inactive when data is transmitted on said communication medium, and is made active when no data is transmitted on said communication medium, said status line being held inactive for a period of time, t(STATUS HOLD), beyond the time data is transmitted, t(STATUS HOLD) being greater than t(DRIVER) to ensure that a transmitting terminal processor and a receiving terminal processor never drive the communication medium at the same time, said terminal processor means including further delay means for delaying transmission of data a period of time, t(TURN HOLD), after said status line becomes active so as to ensure that a receiving terminal processor can send an acknowledge data message to a transmitting terminal processor;

enabling means for automatically enabling said driver upon initiation of data transfer from said terminal processor to the network interface circuit; and

wherein said enabling means includes a driver timer for automatically enabling said driver and continuing to hold said driver enabled until all bits of said data have been transmitted, said enabling means disabling said driver once all bits of said data have been transmitted, said terminal processor re-initiating transfer of the data to the network interface circuit card if an acknowledgment message is not received within a defined time-out period, whereby said enabling means will again automatically enable said driver and continue to hold said driver enabled until all bits of said data have been transmitted, said terminal processor including retransmission delay means for delaying re-initiating transfer of the data so that multiple terminal processors do not retransmit data at the same time.

2. A network interface circuit according to claim 1, said retransmission delay time determined randomly.

3. A network interface circuit according to claim 1, said retransmission delay time determined by an address of the terminal processor.

4. A method for permitting transmission of data between a plurality of terminal processors on a communication medium of a communication network, comprising the steps of:

providing a network interface circuit for electrically interfacing each terminal processor to said network, said interface circuit including a transceiver having a driver for driving said data on said communication medium, a status timer for controlling a status line coupled to said terminal processor, and a driver timer for controlling said driver;

checking said status line to determine if said communication medium is active or inactive, said status line made inactive when data is detected by said status timer;

automatically enabling said driver of said transceiver when data is received from said terminal processor by said driver timer and said status line is active;

continuing to hold said driver enabled until all bits of said data have been transmitted, continuing to drive the communication medium for a period of time, t.(DRIVER HOLD), beyond the time data is transmitted, holding said status line inactive for a period of time, t(STATUS HOLD), beyond the time data is transmitted, t(STATUS HOLD) being greater than t(DRIVER) to ensure that a transmitting terminal processor and a receiving terminal processor never drive the communication medium at the same time, delaying transmission of data by a terminal processor a period of time, t(TURN HOLD), after said status line becomes active so as to ensure that a receiving terminal processor can send an acknowledge data message to a transmitting terminal processor; and

retransmitting said data if an acknowledgment message is not received within a defined time-out period, delaying re-transmission of said data so that multiple terminal processors do not retransmit data at the same time.

5. A method in accordance with claim 4, including the step of further delaying said terminal processor from transmitting data after said status line becomes active so as to allow a receiving terminal to generate an acknowledge data message after having received data.