NRES (Bibirectional IO with pull up resistor)
DISCRETE RT STATUS INPUTS
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.
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.
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.
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.
NVCR (Output)
NSR (Input with pull up resistor)
Service Request.
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.
NSSFLAG (Input with pull up resistor)
Subsystem Flag.
NDATA (Output)
Access to valid data word in real time. Data word available on
T0-T15 during active low signal.
1760 SIGNALS
NCMDSTRB (Output)
NENCHK (Input with pull up resistor)
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.
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)
NDATAST (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.
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.
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.
NENVW (Output)
Signal to transfer Vector word from subsystem to unit in
response to ‘Transmit Vector Word’ mode command via the
T0-T15 highway.
STREL (Output)
NSYNC (Output)
When the store is released from the aircraft all the Remote
Terminal address inputs go high causing signal STREL to go
high.
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.
3
SCDCT2578 REV B 3/11/98
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
