Abstract: A network interface board provides a communication link between a personal computer and a network bus connecting a plurality of programmable logic controllers. The network interface board mounts in an expansion slot of the personal computer. The programmable logic controllers control the operation of various machines. The network interface board includes mailbox registers for storing messages from the network, including three different queues of alarm messages which the personal computer can access in any order. These messages could be in the form of program steps, allowing the personal computer to directly program a programmable logic controller over the communication network.

Abstract: A system allows for transferring messages between microprocessor based devices, such as programmable logic controllers (PLC), and a host computer over an Ethernet communications network. At the host computer level, these messages can be directed globally or locally. The host computer can immediately obtain messages from a programmable logic controller without interruption of the execution of the PLC's ladder program. The host computer can also receive unsolicited messages from the PLC.

Abstract: A control system contains a communications network, a host computer and a programmable logic controller (PLC). The host computer includes prioritized alarm queues for receiving prioritized alarms from the programmable logic controller. Alarms fall into either a local or a global category, and each category supports three types of alarms: warnings, alerts or faults.

Abstract: A control system allows for transferring messages between a programmable logic controller and a host computer over an Ethernet communications network. The messages include a routing address specifying an originating drop number, a destination drop number, and a routing drop number. The system is responsive to the routing address for transferring the messages between the programmable logic controller and the host computer. The host computer can immediately obtain messages from a programmable logic controller without interruption of the execution of its ladder program. The host computer can also receive unsolicited messages from the programmable logic controller.

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.