MIL-STD 1553
on the International Space Station’s
Command and Data Handling System
NSBE training seminar
September 25, 2003
P.Eugene Jackson Jr.
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Command and Data Handling System (C&DH)
ESSMDMs and SSMDMs are used in the Space Station Command and Data Handling
system design which is a “layered” approach providing difference levels of processing and
communication capabilities for each layer. The ESSMDM provide control and data
processing, communication control, and mass resources to support control and management
function of onboard functions. The SSMDM are used to provide embedded control
processing at the lower level and at the main interface to on board sensors and effectors via
analog and discrete input/output.
C&DH Facts: 54 Multiplexer DeMultiplexers ((MDM) – ESSMDM & SSMDM)
100 + MIL-STD-1553 data buses A/B channel redundancy
1200 + MIL-STD-1553 remote terminal (RT) address assignments
• 190 payload 1553 RT addresses
• 600 + International partners and firmware controller
1553 devices
• 90 unique types devices
100 (approximately) Software Interface Control Documents
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Both MDM type are designed to
host User Application Software
(UAS) to control all functionally.
Functional Space Station
Architecture (figure on the left)
represents a”vertical slice” of The
C&DH system defining the Control
Processing, Local Processing,
and the User Processing as they
relate to MDMs. The top two layers,
the Control Buses and the
Local Buses are often referenced to
as Local Bus. The lower layer of
MIL-STD-1553 is referenced
As User Bus layer, because the
communicate Can be either Local
bus protocol or a custom User
Protocol connected directly to the
user equipment.
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Architecture Overview
• Data Rate
1 MHz
• Word Length
20 bits/word
• Data Bits/Word
16 bits
• Transmission Technique
Half-duplex
• Operation
Asynchronous, self-clocking waveform
• Encoding
Manchester II bi-phase
• Bus Topology
Linear multi-drop bus, with stub-coupled
terminals
• Bus Coupling
Transformer or direct coupled
• Transmission Media
Twisted-shielded-pair cable terminated
in its characteristic impedance
• Protocol
Time-division, command/response
• Bus Control
Single or multiple
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MIL-STD-1553 Simple Multiplex
Architecture
Cable
Coupler
Optional
Redundant
Cables
Bus
Controller
Remote
Terminal
Subsystem(s)
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Subsystem
with
Embedded
Remote
Terminal
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Bus Topology Examples
Sensor A
Sensor B
Sensor C
Bus A
Bus B
Single Level
Topology
Comp 1
Sensors
Controls and
Display Bus
Bus A
Bus B
Bus A
Bus B
Navigation
Bus
Single Level,
with Functional
Separation
Bus
Controller
Sensors
Bus A
Bus B
Stores
Bus
Sensors
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Transformer Coupled Bus Network
Terminal
1
Terminal
2
Terminal
N
Stubs
R
1
1
1
1.41
1.41
1.41
R
R
R
R
R
Main Bus
Zo
Zo
R = 0.75 • Zo ohm
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Transmission Line Characteristics
1553 Requirement
• Cable Type
Twisted-shielded-pair
• Capacitance
30 pFd./ft Max
• Characteristic
Impedance
70 to 85 OHMS at 1 MHz, nominal
(actual, per notice 2)
• Attenuation
1.5 db/100 ft Max at 1MHz
• Bus Length
Not specified in 1553B (300 ft suggested max)
• Stub Length
Direct coupled - less than 1 ft
Transformer coupled - 20 ft (suggested max)
• Termination
Ends terminated with resistors of Z0 +/-2%
• Cable Shielding
75% coverage (90% coverage, per notice 2)
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Bus Coupler Characteristics
Direct
Coupled
Transformer
Coupled
Shield
Data Bus
• Isolation resistors: R = 0.75
ZO 2%
• Isolation transformer: turns
ratio 1:1.41 3%
(1 – terminal winding)
At 27v
(1.41 – bus winding) P-P 250-kHz
wave
ZOC > 3K at 75 kHz to 1sq
MHz
1V rms sine wave
Droop: < 20%
Overshooting/ringing: < 1V
CMR: > 45 dB at 1 MHz
• Nominal characteristic
impedance
of bus cable:
ZO = 70 to 85 at 1 MHz
R
R
1:1.41
55 ohm
2%
55 ohm
2%
Transceiver
Transceiver
Terminal
Terminal
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Data Bus Networks—Stub Impedance vs.
Length
2200
•Terminal input impedance (Z1): 1000 ohms, except
where noted
•Coupler transformer: 1:1.41 turns ratio
•Isolation resistors: 52.5 ohms
•Cable capacitance: 30 pF/ft
2000
Stub Impedance, Z1 (ohms)
1800
1600
1400
Transformer Coupled
(Ideal Transformer)
Transformer Coupled
(1553B Transformer)
1200
1000
Direct Coupled
(Z1 = 2000 ohms)
800
600
400
Direct Coupled
200
0
0
2
4
6
8
10
12 14 16 18
Stub Length (ft)
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22
24
26
28
30
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MIL-STD-1553 Data Encoding
One Bit Time
1 MHz
Clock
NRZ
Data
(+) –
(0) –
(+) –
(0) –
(+) –
1
0
1
1
0
0
0
Manchester (0) –
II
Bi-Phase L
(-) –
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MIL-STD-1553B Intermessage Gap and
Response Timing
Bit Time
19
Bit Time
20
1
2
3
Command/Status Sync
Parity Bit
+ Volts
0
– Volts
Gap Time: Min 4.0 microsec
Response Time: Min 4.0 microsec
Max 12.0 microsec
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MIL-STD-1553B Word Formats
•
Command Word
– Command/status sync, 16 data bits, odd party
– Transmitted only by the active bus controller
– Contains unique address of RT or broadcast address (11111)
– Contains transmit or receive data indicator
– Contains subaddress (or mode code indicator)
– Contains word count of 1 to 32 (or mode code)
•
Status Word
– Command/status sync, 16 data bits, odd party
– Transmitted only by the commanded remote terminal
– Contains own address and terminal health information
•
Data Words
– Data word sync, 16 data bits, odd parity
– Transmitted or received by bus controllers or remote terminals
– Received by bus monitors
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MIL-STD-1553B Word Formats
Bit Times
1
2
Command
Word
3
4
5
6
7
8
5
Sync
9 10 11
12 13 14 15 16 17 18 19 20
1
5
Remote Terminal T/R
Address
Subaddress/
Mode
Data Word
Sync
1
Data
P
1
1
3
1
1
1
1
1
Reserved
Busy
Subsystem Flag
Dynamic Bus Control
Acceptance
Terminal Flag
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Parity
1
Broadcast Command
Received
Remote Terminal
Address
16
Service Request
Sync
P
Data Word
Count/Mode Code
Instrumentation
5
1
Message Error
Status
Word
5
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Information Transfer Formats
Controller-toRT Transfer
Receive
Command
Data
Word
RT-toController
Transfer
Transmit
Command
RT-to-RT
Transfer
Receive Transmit
Command Command
Mode Command Mode
Command
Without Data
Word
Mode Command Mode
With Data Word Command
(Transmit)
Mode Command Mode
With Data Word Command
(Receive)
••
••
••
Data
Word
Data
Word
••••
Data
Word
••
Status
Word
Data
Word
Data
Word
••••
••
Status
Word
Data
Word
Data
Word
Status
Word
Status
Word
••
#
Data
Word
Status
Word
#
Next
Command
Word
Data
Word
#
Next
Command
Word
••••
Data
Word
Status
Word
••
Status
Word
Next
Command
# Word
Next
Command
Word
#
#
Next
Command
Word
Next
Command
Word
# Intermessage gap
• • Response time
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Broadcast Information Transfer Formats
Controller-toRT(s) Transfer
RT-to-RT
Transfer
Receive
Command
Data
Word
Receive Transit
Command Command
Mode
Mode Command
Command
Without Data
Word
Mode
Mode Command
With Data Word Command
#
Data
Word
Data
Word
••
••••
Status
Word
Data
Word
Data
Word
#
Data
Word
Next
Command
Word
••••
Data
Word
#
Next
Command
Word
Next
Command
Word
#
Next
Command
Word
# Intermessage gap
• • Response time
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MIL-STD-1553B Terminal Block
Diagram
1553B Data Bus
1553 Terminal
Protocol Control
Internal
Buses
Subsystem
Computer
Transceiver
Encode
Decode
Subsystem
I/F
Transceiver
Subsystem
Encode
Decode
Memory
Power Supply
I/O
Process
Subsystem
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Generalized 1553B Terminal Functions
Word Processor
Data Bus
Interface
A
Analog
Transmit/
Receive
• Receive
–Signal
limiting
–Filter
–Threshold
detection
• Transmit
–Driver
–Transmitter
control
–Timer
• Common
–Bus
coupling
B
Bit/Word
Processor
(Encoder/
Decoder)
• Receive
–Receiver
–Sync
detection
–Data
detection
–Manchester
error
detection
–Parity check
–Bits and
word count
• Transmit
Message Processor
C
Word/
Message
Processor
• Receive
–Command
word code
–Status word
decode
–Address
recognition
–Mode
execution
–Word count
recognition
–Message error
detection
• Transmit
–Transmit
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–Word count
(BC)
–Sync and
D
Subsystem
Interface
Circuits
Subsystem
or Host
Processor
Interface
• Channel
selection
• Data sampling
• Conversation
• Subsystem
timing
• Buffer
registers
• Calibration
• Self-test
• DMA to host
memory
• Interrupt lines
• Control lines
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GNC2 Local Bus – PRESTO analysis
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GNC2 Local Bus – PRESTO analysis - result
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JEM Local Bus – PRESTO analysis (1 of 2)
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JEM Local Bus – PRESTO analysis (2 of 2)
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JEM Local Bus – PRESTO analysis - result
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Mil-Std-1553
Remote Terminal Validation Testing
Requirement: all ORUs connecting to ISS cross-boundary buses must meet
MIL-STD-1553B, Notice 2.
Purpose: to verify that Remote Terminal designed to meet the requirements of
MIL-STD-1553B, Notice 2. Test will be performed on stand-alone ORU.
• Physical Layer: input and output electrical characteristics, noise rejection.
• Protocol Layer: subaddress legalization, error detection and handling,
transmission rate, mode code implementation …..
Test Plan: Appendix A of MIL-HDBK-1553 or Section 100 of MIL-HDBK1553A.
Test Duration: 2 working days allocated for each RT.
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Mil-Std-1553
Remote Terminal Validation Testing
TYPICAL TEST SET-UP
A
Test Support
Equipment
ORU
B
BUS TESTER
PC and Test
Equipment
6
Address
Box
Main Power
Main Power
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Control Moment Gyroscopes
CMG – Facts
The speeds available for commanding: 6269, 6319, 6364, 6410, 6456, 6504, 6552, 660, 6639, 6683, 6722, 6768
6808, 6849, 6890, and 6932 rpm.
The spin motor is used to spin up the wheel and maintain a constant wheel speed. At a nominal line voltage of
120 vdc, the maximum possible wheel speed is 8290 rpm.
Gimbal Torquers – Used to rotate the gimbal assembly.
CMG health and status – Temperatures, electronics voltages, inner and out gimbals positions and rates …
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Control Moment Gyroscope (CMG) interface
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Control Moment Gyroscope (CMG) interface
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Control Moment Gyroscope (CMG) interface
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Control Moment Gyroscope (CMG) interface
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Useful web links
Command and Data Handling Architecture Control Document (D684-10500-02)
http://iss-www.jsc.nasa.gov/ss/issapt/cdhait/resources/add_master15.PDF
Command and Control Software site:
http://iss-www.jsc.nasa.gov/ss/issapt/vehipt/sspt7ipt/cdhipt/ccipt/grp/ccsdev/ccs.htm
MIL STD 1553 tutorial
http://www.condoreng.com/support/downloads/tutorials/index.shtml
MDM User’s Guide ( Volume I)
X8264868, Rev D
MIL-STD-1553
Details drawing contributed by:
Mack McCall, Boeing
Primus E. Jackson Jr.
primus.e.jackson1@jsc.nasa.gov
work 281 488 5551
cell 281 788 7663
.
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