CT2578 / CT2581
SIMPLE REMOTE TERMINAL
FOR MIL-STD-1553 / 1760 & McAir
CIRCUIT TECHNOLOGY
CIRCUIT TECHNOLOGY
www.aeroflex.com/act1.htm
www.aeroflex.com/act1.htm
FEATURES
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Complete RT Protocol
Meets MIL-STD-1553 A/B & MIL-STD-1760
Simple interface
Dual Transceivers (1553 / 1760 or McAir)
+5V only Power Supply
Low Power (0.15 Watts per Channel)
Only validated messages transferred
Optional Data Wrap Around
Store Released Signal
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Packaging – Hermetic Ceramic
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119 Lead, 1.28" SQ. x .16" PGA
84 Lead, 1.645" SQ. x .14" CQFP
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Any Message may be Illegalized
McAir Reduced Response Time Option (inh MC1F)
Optional 1760 checksum
1760 Header word identification
Latched RT Address
MIL-PRF-38534 Compliant Circuits Available
FUNCTIONAL BLOCK DIAGRAM
MANCHESTER DECODER
TRANSEIVER
16 BIT RECEIVE BUFFER
16 BIT TRANSMIT BUFFER
MANCHESTER DECODER
WATCHDOG TIMER
ENCODER / DECODER
REMOTE TERMINAL
STATE SEQUENCER
MANCHESTER DECODER
RT PROTOCOL
TRANSEIVER
16 BIT RECEIVE BUFFER
16 BIT TRANSMIT BUFFER
MANCHESTER DECODER
WATCHDOG TIMER
ENCODER / DECODER
STATUS REGISTER
COMMAND REGISTER
WORD COUNTER
BUS 0
LAST COMMAND REG
BIT REGISTER
BUS 1
CMD / HRD / DATA
STORE RELEASED
HEADER WORD IDENT
1760 CHECKSUM
GENERATION/VALIDATION
1760 OPTIONS
32 WORD
DATA MEMORY
eroflex Circuit T
echnology
– Data Bus Modules For The Future © SCDCT2578 REV B 3/12/98
GENERAL DESCRIPTION
CT2578 is for use in simple Remote Terminal applications
without the need for a processor or software development.
It provides the complete protocol for a Remote Terminal,
supporting all types of message transfers including all 15 mode
codes, with comprehensive error checking. Error handling of
data is not required by the subsystem. The user interface is a 16
bit bidirectional highway with a few control lines.
The low power transceivers are capable of providing the output
voltage required by MIL-STD-1760 and are powered by a +5V
supply.
If sinusoidal (McAir) transceivers are required then the part
number becomes CT2581. This is the only difference between
CT2578 and CT2581.
A 32 word data buffer memory is used to store messages until
validation is complete. Only validated messages are transferred
to the subsystem at a rate of 500 nS per word. Data to be
transmitted is transferred from the subsystem to this buffer
memory at a maximum rate of 1 uS per word. This data memory
may be bypassed in the receive mode and data transferred to the
subsystem on a word by word basis as it is being received.
The device has an optional RT wrap around capability. When
WRAPEN is active, data received at subaddress 1E (30) remains
stored in the data buffer memory (i.e. not transferred to the
subsystem). If followed by a transmit from subaddress 1E the
same data will be transmitted.
There is an option within the device to reduce the response time
in order to conform to other standards such as 1553A and
McAir. In this mode subaddress 1F is allocated a normal
subaddress with subaddress 00 reserved for mode commands.
Any message may be illegalized by applying an active low on the
NME discrete status input. The Remote Terminal will respond
with the Message Error bit set in the status and not use the
information received.
A hardware implementation of the 1760 checksum algorithm
within the device may be enabled via signal NENCHK. When
transmitting, the checksum word is inserted in the last word
position, and when receiving, a valid checksum word will
generate the open drain output (STATUS). The STATUS
output may be hard wired to any of the discrete status inputs (e.g.
Service Request), if it is also hard wired to the input NILLCMD
the device will respond to a failed checksum with the selected
status bit set and not use the data (i.e. not transfer the data to the
subsystem).
In addition to the signal NVCR (valid command word received)
which may be used to illegalize commands, a signal NHDR
(header word received) is available to the subsystem for
verification of the 1760 message header.
The RT address lines are latched on RESET as required by
1760. If all six RT address lines go open circuit the store
released signal (STREL) will go high.
The device is packaged in a 119 pin grid array or 84 lead CQFP
package.
SIGNAL DESCRIPTIONS
1553 / 1760 DATA BUS
DATABUS 0
Signal is connected to the positive side of the external data bus
transformers for bus 0.
NDATABUS 0
Signal is connected to the negative side of the external data bus
transformers for bus 0.
DATABUS 1
Signal is connected to the positive side of the external data bus
transformers for bus 1.
NDATABUS 1
Signal is connected to the negative side of the external data bus
transformers for bus 1.
HARD WIRED
ADDR A-E
(Inputs with pull up resistor)
Remote Terminal address inputs for the unit. ADDR A is the
least significant bit and ADDR E is the most significant bit.
These inputs are internally latched every time the unit is reset.
The latched address information is then compared to the
incoming command word.
ADDR P
(Input with pull up resistor)
Parity bit for the Remote Terminal address inputs. ADDR P
must be set to ODD parity. This input is latched as above.
WRAPEN
(Input with pull down resistor)
Select Remote Terminal wrap around to subaddress 1E. The
Bus Controller sends data to subaddress 1E which remains in the
data buffer memory and is available to be sent back on the very
next command by the Bus Controller. The data in the data buffer
memory in this mode does not get transferred to the subsystem.
If the very next command is not a transmit command to
subaddress 1E, the data buffer memory is flushed and will
respond normally to the next set of commands. If the wrap
around test is enabled, data to subaddress 1E must be transferred
in the correct sequence.
“0" = Normal mode
“1" = Wrap Around mode
MCAIR
(Input with pull down resistor)
This signal sets the unit to respond with a status word within
4 uS (dead bus time). Subaddress 1F is also enabled to be a valid
subaddress for data. Normally subaddress 00 and 1F are
reserved for mode codes.
“1" = 4 uS dead bus response time, subaddress 1F used for data.
“0" = 12 uS response time, subaddress 1F used for mode codes.
C16MH
Z
(Input with pull up resistor)
Free running 16 MH
Z
clock input.
SUBSYSTEM INTERFACE
T0-T15
(Bibirectional IO)
16 bit bidirectional highway to transfer all information to / from
subsystem. The user can also utilise this bus to monitor
Command word and Header word (1760 requirement) for
message illegalization.
SCDCT2578 REV B 3/11/98
2
NRES
(Bibirectional IO with pull up resistor)
Bidirectional reset pin. Interface to this pin should be in the form
of an open collector pull down driver. The unit will be reset
when a low level input is asserted on power up. The pin is
bidirectional in that the unit will drive the signal out low after the
status response of the mode code Reset Remote Terminal. Upon
reset the unit will be able to respond immediately after the rising
edge of NRES.
NILLCMD
(Input with pull up resistor)
Input to illegalize a command to the Remote Terminal with a
clear status response. The signal is sampled after NVCR except
non mode code receive commands in which case it is sampled
after the last data word has been received. A low on this input
will illegalize the message, no transfers to / from the subsystem
will take place. The device will respond with a clear status
unless a bit has been specifically set. No data will be transmitted
following status.
NVCR
(Output)
Early indication that the Remote Terminal has received a
command and the command word is available on T0-T15. This
can be used for message illegalization.
NDATA
(Output)
Access to valid data word in real time. Data word available on
T0-T15 during active low signal.
NCMDSTRB
(Output)
This signal indicates that a completely validated message has
been received for standard subaddress data activity. Mode
commands with or without data will not generate this signal.
The NCMDSTRB signal is 8.5 uS long and is an indication that
a DMA burst will initiate at the end of NCMDSTRB to transfer
words between the 32 word data memory and the subsystem.
The Command word is available on T0-T15 during this period.
NDATAST
(Output)
Signal to transfer normal validated received data from the data
buffer memory to the subsystem at a rate of 500 nS per word via
the T0-T15 highway.
NSSTRB
(Input with pull up resistor)
Signal to transfer normal data for transmission from the
subsystem to the data buffer memory at a maximum rate of 1 uS
per word via the T0-T15 highway.
C1MHZ
(Output)
Free running 1 MHZ clock to subsystem. NSSTRB must be
synchronised to this clock.
NENVW
(Output)
Signal to transfer Vector word from subsystem to unit in
response to ‘Transmit Vector Word’ mode command via the
T0-T15 highway.
NSYNC
(Output)
Signal to subsystem indicating receipt of a synchronise mode
commands If the mode code has an associated data word, it will
be available on T0-T15 at this time. If there is no associated data
word, T0-T15 will be zero.
DISCRETE RT STATUS INPUTS
The following signals are inputs to set the appropriate bits in the
Remote Terminals status word. All inputs are sampled after
NVCR except non mode code receive commands in which case
they are sampled after the last data word has been received. All
status inputs are active low.
NME
(Input with pull up resistor)
Message Error, illegalizes message. No transfers to / from the
subsystem will take place. No data will be transmitted following
the status.
NBUSY
(Input with pull up resistor)
Subsystem Busy. No data will be transferred to / from the
subsystem and no data will be transmitted following status for
non mode code transfers.
NTF
(Input with pull up resistor)
Terminal Flag.
NSR
(Input with pull up resistor)
Service Request.
NSSFLAG
(Input with pull up resistor)
Subsystem Flag.
1760 SIGNALS
NENCHK
(Input with pull up resistor)
Enables / disables the internal hardware checksum generation
and validation. When enabled, the circuitry will check all
incoming data for correct checksum and generate the correct
checksum word for an outgoing data transfer.
“0" = Enable checksum circuitry.
“1" = Disable checksum circuitry.
STATUS
(Open drain output)
Open drain output will toggle high or low on each incoming data
word from the 1553 data bus provided NENCHK is enabled.
When the last data word is received the STATUS line is sampled
by the protocol circuitry to determine if the checksum for the
message is valid. At the end of the message, if STATUS is low
then the checksum is not valid. This STATUS signal can be
wired to several different pins to customise the units response to
a checksum failure. STATUS can be wired to signals such as
NILLCMD and NSR which would cause the message to be
illegalized and set Service Request bit in the Status.
NHDR
(Output)
In Mil-Std-1760, the first data word of a message is defined as
a Header word. The NHDR signal indicates the presence of the
Header word on the T0-T15 highway as it is received. The
Header is also stored in the data buffer memory along with the
complete message.
STREL
(Output)
When the store is released from the aircraft all the Remote
Terminal address inputs go high causing signal STREL to go
high.
SCDCT2578 REV B 3/11/98
3
MESSAGE FORMATS
BC TO RT TRANSFER
DATA BUS
NVCR
NHDR
NDATA
NCMDSTRB
NDATAST
T0-T15
COMMAND
DATA
DATA
DATA
STATUS
1
1.
2.
3.
4.
5.
6.
7.
2
3
4 5 6 7
Valid command word received, contents available on T0-T15 for illegalization purposes.
First valid data word (1760 header word) received, contents available on T0-T15 and stored in 32 word data memory.
Second valid data word received, contents available on T0-T15 and stored in 32 word data memory.
Last valid data word received, contents available on T0-T15 and stored in 32 word data memory. Status bits must be valid within 250nS.
Status register contents transferred to transmit buffer.
NCMDSTRB indicates valid message received, command word available on T0-T15.
Data words transferred from 32 word data memory to subsystem at 500 nS per word.
RT TO BC TRANSFER
DATA BUS
NVCR
NCMDSTRB
NSSTRB
T0-T15
COMMAND
STATUS
DATA
DATA
DATA
1 2 3 4
1.
2.
3.
4.
Valid command word received, contents available on T0-T15 for illegalization purposes. Status must be valid within 600 nS.
Status register contents transferred to transmit buffer.
NCMDSTRB indicates valid message received, command word available on T0-T15.
Data words transferred from subsystem to 32 word data memory at 1 uS per word.
RT TO RT TRANSFER
(RECEIVING TERMINAL)
DATA BUS
NVCR
NHDR
NDATA
NCMDSTRB
NDATAST
T0-T15
REC CMD TRAN CMD
STATUS
DATA
DATA
STATUS
1
SCDCT2578 REV B 3/11/98
2
3
4
4
5 6 7 8
1.
2.
3.
4.
5.
6.
7.
8.
Valid receive command word received, contents available on T0-T15 for illegalization purposes.
Valid transmit command word received, contents available on T0-T15.
Status response of transmitting terminal received.
First valid data word (1760 header word) received, contents available on T0-T15 and stored in 32 word data memory.
Last valid data word received, contents available on T0-T15 and stored in 32 word data memory. Status bits must be valid within 250nS.
Status register contents transferred to transmit buffer.
NCMDSTRB indicates valid message received, command word available on T0-T15.
Data words transferred from 32 word data memory to subsystem at 500 nS per word.
MODE CODES WITHOUT DATA
DATA BUS
NVCR
NRES/NSYNC
When applicable
T0-T15
COMMAND
STATUS
1 2
3
1. Valid command word received, contents available on T0-T15 for illegalization purposes. Status must be valid within 600 nS.
2. Status register contents transferred to transmit buffer.
3. Synchronise mode command, T0-T15 = 0.
MODE CODES WITH DATA RECEIVE
DATA BUS
NVCR
NDATA
NSYNC
When applicable
T0-T15
COMMAND
DATA
STATUS
1
1.
2.
3.
4.
2 3 4
Valid command word received, contents available on T0-T15 for illegalization purposes. Status must be valid within 600 nS.
Valid data word received, contents available on T0-T15. Synchronise data word stored in 32 word data memory.
Status register contents transferred to transmit buffer after message validation.
Synchronise data word(when applicable) transferred from 32 word data memory to main memory and available on T0-T15.
MODE CODES WITH DATA TRANSMIT
DATA BUS
NVCR
NENVW
When applicable
T0-T15
COMMAND
STATUS
DATA
1 2 3
1. Valid command word received, contents available on T0-T15 for illegalization purposes. Status must be valid within 600 nS.
2. Status register contents transferred to transmit buffer after message validation.
3. Vector word (when applicable) transferred from subsystem to transmit buffer.
SCDCT2578 REV B 3/11/98
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