Abstract: Devices in a process control system communicate by data messages over a communication medium segment. Each device includes a communication controller that includes a data queue and a queue of received message objects. The data queue stores a plurality of messages received on the communication medium. The received message objects contain information about a corresponding message in the data queue.

Abstract: Devices in a process control system communicate by data messages over a communication medium segment. Each device includes a communication controller that maintains an order of occurrence of events received from and transmitted to a communication medium. The communication controller includes an order of occurrence identification (OOO_ID) counter and an event queue memory. The event queue memory sequentially stores an event type identifier for each event that is processed by the communication controller. The OOO_ID counter provides an OOO_ID to associate with each event type identifier.

Abstract: Devices in a process control system communicate by data messages over a communication medium segment. Each device includes a communication controller that includes a received data memory and a plurality of received message objects. When a message is received, a received message object is activated, and the initial position of a write pointer in the received data memory is stored in the received message object. During message reception, if a hardware device determines that the message is to be ignored, the received message object is deactivated, thereby preventing further writing of the message to the received data memory. The write pointer is then preferably returned to its initial position as stored in the received message object.

Abstract: Devices in a process control system communicate by data messages over a communication medium segment. Each device includes a communication controller that automatically time stamps events associated with received and transmitted messages.

Abstract: A device on a process control network transmits scheduled messages at periodic intervals and unscheduled messages between scheduled message transmissions. A dynamic time remaining value is produced by subtracting a current timer value from a next scheduled event time each time the timer is incremented. If the time required to transmit an unscheduled message is greater than the time remaining value, the message is not transmitted.

Abstract: A communication controller in a device on a network automatically prevents transmission of data onto the network in response to a transmit request from a CPU of the device if a message is being received or has been received but not read or acknowledged.

Abstract: A diagnostic tool has a packet based network medium attachment unit, a measurement interface, a network interface, and a microprocessor for reading DLPDUs from a network segment and for taking simultaneous measurements of DLPDUs on the segment. The measurement data is associated with a stored DLPDU if the DLPDU is still active on the network segment when the measurement data is read by the microprocessor. The diagnostic tool utilizes a currently active attribute to determine the status of a DLPDU.

Abstract: The system has a control center, a time master device and a plurality of distributed, time slave field devices in synchronization with a master clock of the time master device. The time master device periodically transmits a time distribution data unit. Each time slave field device has a timer adjustment element, a fixed rate clock and a variable clock. The timer adjustment element calculates a frequency ratio between the master clock and the fixed rate clock and uses the frequency ratio to calculate adjustment coefficients to adjust a local sense of time for each field device, such that a time stamp of each field device is synchronized to the master clock.

Abstract: A wiper control system which includes dual wiper control circuits operating from a single rotary control switch, which is mounted in a cockpit of an aircraft remote from the rest of the wipers and system components which are mounted near an aircraft windscreen in a housing from which a motor converter drive shaft protrudes generally normal to a portion of the airframe surface. The drive shaft is connected to one end of a wiper arm and the second end of the wiper arm is rotatably attached to the wiper blade. The dual wiper control circuits are electrically isolated from each other. The rotary switch includes dual voltage dividers and a single axial rotating member to create an analog voltage output signal representative of the control switch position which is interpreted by a controller circuit. The rotary switch speed selections include a HIGH speed, a LOW speed, an INTERMITTENT delay selection, and also a selection for PARK and OFF.