Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
1998-12-16
2001-02-27
Shin, Christopher B. (Department: 2782)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S025000, C710S106000, C359S107000
Reexamination Certificate
active
06195768
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to asynchronous, serial digital data buses and, more particularly, to a system and method for monitoring data on a high speed fiber-optical data bus.
BACKGROUND OF THE INVENTION
A data link, data bus, or data network is an array of data transmitters and receivers arranged to transmit data bi-directionally between two or more users over wire, optical fiber, or another transmission medium. Diagnostic instruments that monitor, process, and display the data communicated over these links, buses, or networks are necessary for integrating and trouble shooting complex systems. A bus monitor is one such diagnostic instrument that receives data transmitted over a data link, data bus, or data network and extracts selected information to be displayed or otherwise used. For example, the bus monitor may be connected to a host computer that displays the data in various formats to aid in solving various integration problems. In military aircraft applications, a bus monitor is commonly used as flight test instrumentation to verify data bus performance and/or the performance of a subsystem attached to the bus.
One type of data bus used in aerospace applications is the SAE AS1773 20 Mbps multiplexed command/response fiber-optic data bus. As is known to those skilled in the art, MIL-STD-1773, entitled “Fiber Optics Mechanization of an Aircraft Internal Time Division Command/Response Multiplex Data Bus,” is a 1 Mbps fiber-optic version of the popular 1 Mbps copper wire MIL-STD-1553 data bus, and provides the option of using fiber-optics in military avionics systems in place of MIL-STD-1553. MIL-STD-1553 defines a serial asynchronous data bus employing Manchester encoding on which the messages are time multiplexed among users, allowing several users (nodes) to share the same resource (transmission medium) by using it at different times. MIL-STD-1773 specifies a 1 Mbps protocol that is identical to MIL-STD-1553, with the difference confined to the transmission medium. MIL-STD-1773 specifies a fiber-optic medium, while MIL-STD-1553 specifies an electrical medium. AS1773 includes both 1 Mbps and 20 Mbps protocols. The 20 Mbps fiber-optic AS1773 data format is identical to the 1 Mbps format, except that the rate of data transmission is substantially higher, and the AS1773 protocol differs in having a preamble before each message to aid in recovering the clock at the higher data rate. The AS1773, MIL-STD-1773, and MIL-STD-1553 data buses all use Manchester encoded data (Manchester II bi-phase level) to send messages of up to 33 words, each consisting of 16 data bits followed by a single parity bit and preceded by a characteristic synchronization pulse that consists of an easily recognizable illegal Manchester pattern.
Use of the 20 Mbps AS1773 bus has heretofore been limited because there is no conventional diagnostic instrument available to provide a monitoring function for this high speed fiber-optic data bus. Such test instrumentation is necessary to integrate equipment into applications, for example aircraft control systems. The 20 Mbps AS1773 bus provides a twenty times speed advantage over the popular MIL-STD-1553 bus and the additional advantages of being immune to Electro-Magnetic Interference (EMI), as well as not being a source of EMI. The AS1773 bus was developed primarily for space applications, so the components are designed to provide the additional benefit of being immune to single event upsets due to ionizing radiation. In order to increase the ease of integrating the 20 Mbps AS1773 data bus into various applications, it would be desirable to provide a system and method for monitoring a high-speed data bus of the serial, asynchronous type employing Manchester encoding, which provides a means to monitor the data transmitted at such a high data rate. Preferably, the system would retrieve messages from the data bus and store the messages for processing and analysis.
SUMMARY OF THE INVENTION
A system and method for monitoring a high speed data bus which transfers data and commands and is of the serial, asynchronous type employing Manchester encoding is described herein. A bus monitor preferably includes a fiber-optic receiver that provides communication with the bus for receiving and processing message data from the bus, a logic device that receives and processes the message data, and a memory device adapted to store data and commands received via the bus. The bus monitor is particularly advantageous for use with a data bus employed according to the AS1773 data bus protocol.
The fiber-optic receiver preferably receives the optical signal from the data bus, converts the optical signal into an electrical waveform, and transmits the electrical waveform to the logic device. The logic device preferably receives the electrical waveform from the fiber-optic receiver, performs logical sequences, and sequentially transmits message words to the memory device. The memory device preferably receives the message words from the logic device, sequentially stores the message words, and permits the stored data to be accessed by a host computer.
Preferably, the system of the present invention monitors messages transmitted on a high speed, serial, asynchronous data bus employing Manchester encoding, wherein the data bus transmits the messages as a sequence of optical signals, the messages containing command, status, and data words. The preferred system includes an fiber-optical receiver connected to the data bus and adapted to receive the optical signals. The fiber-optical receiver converts each optical signal into an electrical signal which constitutes a message word containing either a command word, a status word, or a data word and sends the message word into a logic device. The system also preferably includes a memory device having a number of storage locations adapted to receive and store the message words. Preferably, the memory device is organized in an optimal fashion to allow the system to monitor high speed data buses. Preferably, the logic device is operationally coupled to the fiber-optical receiver and adapted to receive and process message words serially. The logic device controls the transfer of each message word into one of the memory locations of a message buffer. The logic device also generates an address word for each of the transferred command and status words representing the address within the message buffer holding a particular command or status word. The logic device stores this command word address or status word address into one of the memory locations of a pointer table. As each message consists of a command word or a status word followed by a number (0-32) of data words, the entries in the pointer table indicate the first word of each message stored into the message buffer.
In a preferred embodiment, the logic device senses the end of a message and stores a time stamp and the next pointer address into the next memory location of the pointer table. The time stamp is preferably stored at the same time that the logic device is storing the next command or status word address and is stored into the high word of the long memory word holding the command or status word address.
The memory device is preferably coupled to a host computer capable of analyzing, processing and displaying the received message words and information about the received message words that aid in system integration and diagnosis of system faults. The logic device and the host computer interact in the processing of the data. For example, the logic device may signal the host computer (e.g., via an interrupt) when either the message buffer or the pointer table is full. The logic device may pause at this time, to allow the host computer to read and process the data. Alternatively, the logic device may continuously transfer message words into the message buffer. In this embodiment, the host computer preferably reads and processes the message words in a rotating buffer memory sufficiently fast such that stored data is processed before it is overwritten by subseq
Bryan Cave LLP
Crowe Daniel A.
Shin Christopher B.
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