LAN interface which permits a host computer to obtain data without interrupting a ladder program executing in the interface

• US 5,151,978 A
• Filed: 03/22/1990
• Issued: 09/29/1992
• Est. Priority Date: 03/22/1990
• Status: Expired due to Term

• Current Assignee: Schneider Automation Incorporated (Schneider Electric SE)
• Original Assignee: Square D Company (Schneider Electric SE)
• Inventors: Bronikowski, Joseph T., Hill, Brian T., Sackmann, David J., Weber, Mark S.
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): Harrell, Robert B.
• Application Number:
  US07/497,451
• Time in Patent Office: 922 Days
• Field of Search: 364/200, 364/900, 364/DIG. 1, 364/DIG. 2, 395/200, 395/250, 395/275, 395/325, 395/800
• US Class Current: 709/216
• CPC Class Codes: G05B 19/052 Linking several PLC's
• CPC Class Codes: G05B 19/054 Input/output
• CPC Class Codes: G05B 19/058 Safety, monitoring
• CPC Class Codes: G06F 13/128 for dedicated transfers to a network for protocol converters G06F13/387

Abstract

A control system allows for transferring messages between a programmable logic controller and a host computer over a serial data communications network. The programmable logic controller executes a ladder program and has an integral network interface module for permitting direct communicative coupling to the communications network. Messages can be received and sent by the programmable logic controller without interruption of the execution of the ladder program. The programmable logic controller can receive unsolicited messages from the host computer.

Claims

1. A programmable logic controller for communication on a high speed serial data communication network, said programmable logic controller having means for executing a ladder program and including integral means for directly coupling to said communications network, said programmable logic controller comprising:

(a) first port, said first port adapted to couple to said communications network;

(b) a communications processor coupled to said first port;

(c) a random access memory means coupled to said communications processor for storing messages from said communications network as a mailbox register;

(d) a data bus;

(e) a scan processor means coupled to said data bus for executing said ladder program;

(f) an image table coupled to said data bus, said image table having means for storing data directly from said communication network for use by said scan processor means and means for storing data from said scan processor means for use by said communication network;

(g) a two port RAM having a first port coupled to said communications processor and a second port coupled to said data bus;

(h) a control processor means coupled to said data bus for controlling said storing means of said image table and for transferring data between said image table and said mailbox register or said communications network through said two-port RAM; and

(i) wherein said first port, said communications processor, and said mailbox register combine to form said integral means for directly coupling said programmable logic controller to said communications network, said integral means functioning as an equivalent network interface module.

2. The programmable logic controller of claim 1 wherein said mailbox registers receive unsolicited messages from said communications network without interrupting the execution of said ladder program by said scan processor means.

3. A programmable logic controller (PLC) for communicatively coupling to a data communications network to send and receive messages, said PLC comprising:

(a) a data bus;

(b) a scan processor means coupled to said data bus for executing a ladder program;

(c) a control processor coupled to said data bus;

(d) an image table coupled to said data bus;

(e) an equivalent network interface module including a communications processor and a first port, said first port adapted to coupled to said communications network; and

(f) a multiport RAM coupled between said data bus and said equivalent network interface module.

4. The PLC of claim 3 wherein said equivalent network interface module includes a mailbox register for receiving unsolicited messages from said communications network without interrupting the operation of said scan processor.

5. The PLC of claim 3 wherein said messages include routing addresses and said equivalent network interface module includes means responsive to said routing addresses for directing said messages to either said mailbox register or said image table.

6. The PLC of claim 3 wherein said communications network is in Ethernet data network.

7. The PLC of claim 3 wherein said communications network exhibits non-deterministic behavior and said PLC includes means for limiting said nondeterministic behavior.

8. The PLC of claim 7 wherein said nondeterministic behavior limiting means comprises means for specifying a maximum time for waiting for receipt of a message.

9. The PLC of claim 7 wherein said nondeterministic behavior limiting means comprises means for specifying a maximum time for waiting for a reply.

10. In a programmable logic controller having a scan processor and a control processor for executing a series of program steps, an improvement for permitting direct communicative coupling of the programmable logic controller to a high speed data communications network, the improvement comprising:

(a) an equivalent network interface module, said equivalent network interface module including a communications processor, a random access mailbox and a first port coupled to said communications processor, said first port adapted to couple directly to said high speed communications network;

(b) a multi-port RAM coupled between said control processor and said equivalent network interface module, said multiport RAM including means for exchanging data between said equivalent network interface module and said control processor, said data having use in said program steps;

(c) wherein said programmable logic controller can receive an uncritical, unsolicited message from said high speed communications network without interruption of said execution of said series of program steps; and

(d) wherein said programmable logic controller can receive a critical, unsolicited message from said high speed communications network with interruption of said execution of said series of program steps.