MIL1553.OCT–UTMC–pm
Jumping aboard the MIL-STD-1553 bus
MIL-STD-1553 simplifies the implementation of a rugged monitoring and
communications system
BY TONY JORDAN United Technologies Microelectronics Center Colorado
Springs, CO
The MIL-STD-1553B data bus is designed to allow for multisensor
communication in military or other tough applications such as
environmental monitoring systems, industrial process controls, avionics
(cockpit displays, for example), and exploratory spacecraft experiment
systems. Based on a single CPU, the bus has the important advantages of
reducing system size, weight, and complexity. Several 1553B architectures
are available for the various applications. A typical architecture would
include a single serial bus controller and multiple serial bus interfaces
(remote terminals). The bus controller is responsible for initiating all
commands on the bus, while the serial bus interface interprets and
responds to these commands. A bus controller command normally triggers
the transmission of sensor data. In a distributed-system architecture with
remote terminal interfaces linking the data sensors to a data bus (see
Fig. 1a), the number of remote terminals is dictated by the number of
data-collecting sensors. An alternative concentrated system architecture
uses a common remote terminal interface to link multiple data-collecting
sensors to a serial bus (see Fig. 1b). This approach is especially useful
when monitoring multiple multiparameter systems like multiple engines or
systems. During data collection, the bus controller requests the
transmission of data from a specific sensor. Physical location or size may
limit the latter system configuration. Most of the data-collecting
applications discussed here require the conversion of real-time analog
information into digital information by an A/D converter for processing by
the main CPU. The digital information is then stored in memory and shared
by the A/D converter and remote terminal interface. The remote terminal
accesses memory when instructed by the bus controller to transmit the
latest sensor information. Figure 2 shows an example of a
sensor-to-remote-terminal interface. The support electronics facilitates
the sharing of memory between the A/D converter and the remote terminal
interface. Key to implementing this architecture is the control and
reduction of the cost of sensor electronics. The latest 1553B remote
terminal interface devices configure themselves from operation on the
serial bus after power-up and master reset. Autonomous operation of the
sensor and the A/D converter allows for the elimination of a host
microcomputer in the sensor electronics. This not only reduces board
complexity, but also eliminates software requirements. To do this, an
auto-initializing remote terminal interface device, such as UTMC's UT69151
Smicronsmit (see Fig. 3), must be integrated into the system design. The
bus controller, typically embedded in the main CPU electronics, initiates
all data transfer from the remote terminals. The main CPU, such as an Intel
i960, Mips Computer R3000, or Motorola 68332, is responsible for
initiating all data transfers occurring on the serial bus and for
processing the transmitted information. In a MIL-STD-1553B system
architecture, the main CPU instructs the bus controller to command the
remote terminal to transmit sensor information. For example, in the
systems shown in Figs. 1a and 1b, data are collected and processed by the
main CPU, via the bus controller. The data are then shown for user
interpretation in the graphical display unit or used by the main CPU to
adjust the system operation or performance. The bus controllers are
configured by the main CPU to transmit messages commanding sensor
information at a rate that can sustain the update of graphically displayed
parameters or data required to control system operation.
Periodic data collection Periodic data collection is accomplished by
using a minor and major frame message schedule technique. Minor frames,
which are a finite set of messages at a fixed rate, are executed by the
bus controller at a defined rate to ensure the proper collection and
update of system parameters. The linking of multiple minor frames to
create a major frame (see Fig. 4) will support multiple multiparameter
system monitoring. A range of MIL-STD-1553B controllers is available from
a host of manufacturers, including UTMC, GEC Plessey, National Hybrid,
Aeroflex Microelectronics, Northern Telecom, and ILC Data Device Corp.
Reducing sensor electronics cost by creating microcomputer-less serial bus
interfaces increases the main CPU's software overhead and can increase the
amount of data transmitted on the bus. An example where large amounts of
raw data may limit a centralized system is image processing. Designers
must carefully study the amount of data required to implement the system
and compare this to the serial bus bandwidth and utilization. In many
cases, it is better to transmit raw data over the serial bus and have the
processing performed by the main CPU. However, the amount of data and bus
bandwidth may be limited by this architecture in certain instances. To
implement a low-cost data-collection system, it is important to understand
the tradeoffs between distributed data processing at the sensor versus
central processing via the main CPU.
CAPTIONS:
Fig. 1. In a distributed-system architecture, the number of remote
terminals determines the number of data-collecting sensors (a). An
alternative to a distributed architecture uses a common remote terminal
interface to link multiple data-collecting sensors to a serial bus (b).
Fig. 2. In a sensor-to-remote-terminal interface, the support electronics
facilitates the sharing of memory between the A/D converter and the remote
terminal interface.
Fig. 3. UTMC's UT69151 Smicronsmit is an auto-initializing remote
terminal interface device that helps to reduce board complexity and reduce
the overhead on the CPU.
Fig. 4. The linking of multiple minor frames to create a major frame will
support multiple multiparameter system monitoring.
The following companies are mentioned in this article. For more
information, call the companies or circle the reader service numbers.
Aeroflex Microelectronics Plainview, NY John Buyko 516-694-6700
GEC Plessey, Semiconductor Div. Scotts Valley, CA Scott Gardner
408-438-2900
ILC Data Device Corp. Bohemia, NY Mike Glass 516-567-5600
National Hybrid location contact
Northern Telecommunication location George Sponsler
United Technologies Microelectronics Center Colorado Springs, CO
Anthony Jordan 719-594-8000
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