Datasheet

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Debugging Serial Buses in Embedded System Designs
How It Works
MIL-STD-1553 asynchronously transmits messages of up to
thirty-two 16-bit data words at bit rates of up to 10 Mb/s over
shielded twisted-pair and twinax cabling. A 1553 network
uses time-division multiplexed half-duplex communication
to transmit data over a single cable. For safety-critical
applications, dual redundant buses are commonly used
to provide higher-reliability communications. Manchester
II bi-phase encoding is used to allow direct or transformer
coupling. Manchester encoding is self-clocking, independent
of the bit sequence, and is DC-balanced. Because the
information in Manchester coded signals is actually contained
in the polarity and timing of the zero-crossings, the 1553 bus
is tolerant of large variations in signal levels.
MIL-STD-1553 defines three distinct word types: Command
words, Data words, and Status words. All are twenty-
bit structures, with a 3-bit synchronization field, a 16-bit
information field, and finally an odd parity bit for simple error
detection. The sync field is an invalid Manchester signal, with
a single transition in the middle of the second bit time. A
command/status sync has a negative transition in the middle,
while a data sync has a positive transition.
Command words, sent by the active bus controller, specify
the function that a remote terminal is to perform. The 16-
bit information field contains a 5-bit terminal address which
uniquely identifies the terminal, a transmit/receive bit, 5 bits
of sub-address or mode, and 5 bits of word count or mode
code.
Data words, transmitted by either a bus controller or remote
terminal, are sent with the most-significant-bit first.
MIL-STD-1553
Background
Similar to the computer industry’s LAN, MIL-STD-1553 is
a military standard that defines the electrical and protocol
characteristics of a serial bus initially designed for data
communication in avionics applications.
MIL-STD-1553 began with the development of the A2-K draft
standard by the Society of Automotive Engineers (SAE) in
1970. After government and military reviews and revisions, it
was released as MIL-STD-1553 (USAF) in 1973. MIL-STD-
1553A was released in 1975 to support all of the branches of
the military, and the SAE then released and froze the MIL-STD-
1553B standard to enable component manufacturers to build
compliant products. The most recent changes, documented
as Notice 2, was released in 1986 to provide a common set of
operational characteristics. The standard is now overseen by
SAE as commercial document AS15531.
Although the standard was widely used in US military
applications, it has also been used commercially in mass-
transportation, spacecraft, and manufacturing applications,
and has been accepted and implemented by NATO and many
other governments.
Command
Word Sync
Terminal
Address T/R
Subaddress /
Mode
Word Count /
Mode Code Parity
Bits 3 5 1 5 5 1
Figure 36. MIL-STD-1553 Command Word Format.
Data Word Sync Data (D15 – D0) Parity
Bits 3 16 1
Figure 37. MIL-STD-1553 Data Word Format.