Pulse or digital communications – Transceivers
Reexamination Certificate
1998-09-23
2001-04-03
Chin, Stephen (Department: 2634)
Pulse or digital communications
Transceivers
C455S073000, C710S100000
Reexamination Certificate
active
06212224
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to digital logic design. More specifically, it relates to a bi-directional bus buffer that is designed to operate according to the specifications of the MIL-STD-1553B data bus standard. Reference may be made to “MIL-STD-1553B: Department of Defense Interface Standard for Digital Time Division Command/Response Multiplex Data Bus”, Sep. 21, 1978.
BACKGROUND OF THE INVENTION AND DESCRIPTION OF PRIOR ART
The United States Department of Defense requires the use of MIL-STD-1553B as the standard for communications between electronic modules on all military airplanes and other vehicles. MIL-STD-1553B defines an asynchronous serial, command/response digital data bus on which messages are time division multiplexed among users. The 1553 STD specifies all of the electrical characteristics of receivers, as well as the complete message transmission protocol. The 1553 protocol specifies that all continuous data transfers start with a positive excursion of the wave form from a null bus condition (no significant signal present). The 1553 protocol further requires a “no response time out” of 14 microseconds and a 12-microsecond maximum allowed for remote terminal (RT) response time. This system will therefore not tolerate an additional signal propagation delay of more than 2 microseconds. The transmission medium is a twisted wire cable pair. The standard uses bi-phase Manchester II encoded signals for which timing of the zero-crossing signals is critical.
There is a need in the art to permit several 1553 remote terminals to be operated on a secondary bus that forms a stub off of a main bus. There is a further need to permit the use of the 1553 standard in a system where the length of a single main bus, or the loading on it, might cause the bus performance to become marginal or undependable. Finally, there is a need to permit the extension of a 1553 application to farther locations without modifying an existing physical bus structure.
In order to satisfy such needs in the art, signal repeaters have been devised to extend the application of the 1553 standard. For the purposes of this application, a repeater is a device that receives an encoded input data signal from a first bus, decodes and stores the data temporarily, then encodes and retransmits the data out on a second bus. Such a repeater is produced by Cal Corporation of 1050 Morrison Drive, Ottawa, Ontario, Canada. However, these devices have specific disadvantages in terms of high data latency and messaging complexity, requiring additional software/firmware and more complex electronics than the present invention. Furthermore, such repeaters are unable to work within the 1553 specifications due to the long propagation delay (more than 2 microseconds) through the repeater. There is therefore a demand for a device that will meet the needs described above, while staying within the 1553 specifications.
SUMMARY OF THE INVENTION
The present invention is a bi-directional buffer/driver that meets the needs described above. The new buffer/driver is designed to operate in a bi-phase Manchester II encoded communication system with a differential bi-directional data bus using a single wire pair in accordance with specifications of MIL-STD-1553B. A buffer, unlike a repeater, does not decode or encode data. A buffer receives an encoded input data signal from a first bus, reshapes and amplifies the signal, and then retransmits the signal out on a second bus.
The output of the present buffer/amplifier drives the bus with the proper characteristics so that it is transparent to both the remote terminals and the main bus controller. As will be further described herein, the new bus buffer receives Manchester bi-phase encoded data, reconstitutes the received data signal, and transmits the reconstituted signal between a main bus and a secondary bus in either direction. Thus, an existing bus may be extended beyond the previous maximum communication distance without modifying the bus elements already installed.
Specifically, it is the object of the present invention to provide a MIL-STD-1553B buffer/driver which:
1. Presents impedance to the original main bus equal to that of a standard remote terminal.
2. Operates over the normal voltage operating range identified for a remote terminal in MIL-STD-1553B.
3. Reconstitutes the voltage waveform to full terminal output voltage as specified at point “A” of MIL-STD-1553B.
4. Stabilizes the zero-crossings of its output signal to be spaced in time by multiples of 500 nanoseconds, as specified by MIL-STD-1553B, when a distorted input has zero-crossings that are spaced within ±150 nanoseconds of a multiple of 500 nanoseconds, as permitted by MIL-STD-1553B.
5. Passes the reconstituted waveform on to a secondary bus to which the additional remote terminals are connected through stubs.
6. Contains input and output MIL-STD-1553 compliant transformers on each port.
7. Operates autonomously (needs no control input from any other device to function within a MIL-STD-1553B bus structure).
8. Senses the direction of traffic between the main bus and the secondary bus.
9. Operates on the data sequentially, i.e. on a first-come-first-served basis, such that the first of the main or secondary inputs to receive a signal controls the direction of the bus buffer, and the direction will not change until a null bus condition (no significant signal present) occurs.
10. Detects a null bus condition within 750 nanoseconds of the input bus returning to a value less than the receiver thresholds, and thus allows the bus buffer to reset for the next data transmission in either direction.
11. Receives and retransmits a data signal through the bus buffer with a propagation delay of less than one microsecond, so that the use of the buffer in systems containing remote terminals, which require up to 12 microseconds to respond with a status word, will not cause the total delay to exceed the “no response” timeout of 14 microseconds.
12. Provides a total system two-way delay due to the addition of the bus buffer that is less than 2 microseconds.
13. Does not decode or encode data, but only receives, reconstitutes, and retransmits a Manchester wave form that is transferred through it.
To fulfill the above-stated objects of the invention, the applicant has invented a serial bus buffer for conditioning and amplifying bi-directional electrical signals on a line carrying MIL-STD-1553 bi-polar signals, comprising: a receiver including a threshold detector, a signal conditioner including a retiming circuit, and a transmitter including an amplifier. The receiver is connected to the signal line at a first bus. A threshold detector within the receiver is responsive only to incoming bi-polar line signals having a pre-selected minimum positive or negative amplitude thus producing a filtered signal output. A signal conditioner receives the filtered bi-polar signal output from the receiver and comprises means for converting the filtered bi-polar signals into a first and second alternating uni-polar digital signals, one of the uni-polar signals having the timing of the positive excursion of the bi-polar signal beyond the minimum magnitude and the other uni-polar digital signal having the timing of the negative excursion of bi-polar signal beyond the minimal magnitude, each of the uni-polar signals having only two states, a zero-voltage state and a positive-voltage state. The signal conditioner further includes means for increasing the positive-voltage state period of each uni-polar signal pulse from the end of its positive-voltage state to the beginning of the next positive voltage state of the other uni-polar signal pulse so that no zero voltage state of either signal occurs at the same time. A timing circuit within said signal conditioner includes a periodic signal sampler having a clock and a logic circuit applied to each of the uni-polar signal outputs of the signal conditioner, producing digital outputs of “+1” or “−1” respectively when the positive-voltage state of the first or second uni-polar signal
Cammarota Joseph P.
McGlynn Edwin F.
Chin Stephen
Fan Chieh M.
Gore Gregory J.
M Technologies, Inc.
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