MODE CODES WITH DATA RECEIVE BROADCAST
DATA BUS
NVCR
NDATA
NSYNC
When applicable
T0-T15
COMMAND
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. Valid data word received, contents available on T0-T15. Synchronise data word stored in 32 word data memory.
3. Synchronise data word (when applicable) transferred from 32 word data memory to main memory and available on T0-T15.
REMOTE TERMINAL DETAIL
COMMAND REGISTER
RESVD
Reserved: set to zero
BCST
Broadcast Command Received: set internally.
BUSY
Subsystem Busy: set with a discrete pin.
The five most significant bits of the command register contain the
Remote Terminal Address.
Bit 10 of the register is the Transmit / Receive bit. If it is set to '1'
the device will perform the transmit sequence and it is set to '0' it
will perform the receive sequence.
Bits 5 to 9 contain the Subsystem Address but two of these
addresses are reserved and one programable. 11111 (1F) or 00000
(00) indicate that the command is a mode code. The least
significant five bits of the command register are used to decode the
mode code and are not used as the word counter as a mode code
may only have a maximum of one associated word.
111110 (1E) and WRAPEN sets the sequencer up to perform the
wrap around function.
The least significant five bits of the command register contain the
number of data words to be transmitted or received. 11111 is 31
words and 00000 is 32 words.
STATUS REGISTER
SSFL
Subsystem Flag: set with a discrete pin.
DBCA
Dynamic Bus Control Acceptance: set to zero.
TF
Terminal Flag: set with a discrete pin.
The status register is cleared and the external bits loaded on all
commands except 'Transmit Status' and 'Transmit Last Command'.
The external status bits (both discrete and programable) must be
valid 600 nS from the rising edge of NVCR for transmit commands
and mode codes, and 250 nS from the rising edge of NDATA for
the last data word in a receive message.
If discrete status inputs are not used they may be left open circuit.
STATUS RESPONSE TIME
The response time (all commands) measured from the mid bit zero
crossing of the last bit of the last word to the mid bit zero crossing
of the status word sync is nominally 11.0 uS.
This time period is used to monitor for more data words on the bus.
If a valid sync field followed by four valid Manchester bi-phase bits
are detected then this is considered to be another word on the bus.
ME
Message Error: set internally as a result of an error in the received
message or set externally with a discrete pin to illegalize a
message.
INST
Instrumentation: set to zero.
SR
Service Request: set with a discrete pin.
The response time may be reduced to 6.0 uS (4.0 uS dead bus
time) by setting the MCAIR input active high.
MESSAGE ILLEGALIZATION
Any command or mode command may be illegalized by setting the
NME input active low. The remote terminal will respond with
status with the Message Error bit set, provided the message was
valid, and not use the information received. There will be no
transfers to or from the subsystem.
SCDCT2578 REV B 3/11/98
7
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
