CT1990 データシートの表示（PDF） - Aeroflex Corporation
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CT1990
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CT1990 Datasheet PDF : 29 Pages
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REMOTE TERMINAL OPERATION
Receive Data Operation
All valid data words associated with a valid receive data command word for the RT are passed to the subsystem.
The RT examines all command words from the bus and will respond to valid (i.e. correct Manchester, parity
coding etc.) commands which have the correct RT address (or broadcast address if the RT broadcast option is
enabled). When the data words are received, they are decoded and checked by the RT and, if valid, passed to
the subsystem on a word by word basis at 20 µs intervals. This applies to receive data words in both Bus
Controller to RT and RT to RT messages. When the RT detects that the message has finished, it checks that the
correct number of words have been received and if the message is fully valid, then a Good Block Received
signal is sent to the subsystem, which must be used by the subsystem as permission to use the data just
received.
The subsystem must therefore have a temporary buffer store up to 32 words long into which these data words
can be placed. The Good Block Received signal will allow use of the buffer store data once the message has
been validated.
If a block of data is not validated, then Good Block Received will not be generated. This may be caused by any
sort of message error or by a new valid command for the RT being received on another bus to which the RT
must switch.
Transmit Data Operation
If the RT receives a valid transmit data command addressed to the RT, then the RT will request the data words
from the subsystem for transmission on a word by word basis. To allow maximum time for the subsystem to
collect each data word, the next word is requested by the RT as soon as the transmission of the current word
has commenced.
It is essential that the subsystem should provide all the data words requested by the RT once a transmit
sequence has been accepted. Failure to do so will be classed by the RT as a subsystem failure and reported as
such to the Bus Controller.
Control of Data Transfers
This section describes the detailed operation of the data transfer mechanism between the RT and subsystems.
It covers the operations of the signals DTRQ, DTAK, IUSTB, H/L, GBR, NBGT, TX/RX during receive data and
transmit data transfers.
Figure 7 shows the operation of the data handshaking signals during a receive command with two data words.
When the RT has fully checked the command word, NBGT is pulsed low, which can be used by the subsystem
as an initialization signal. TX/RX will be set low indicating a receive command. When the first data word has
been fully validated, DTRQ is set low. The subsystem must then reply within approximately 1.5 µs by setting
DTAK low. This indicates to the RT that the subsystem is ready to accept data. The data word is then passed to
the subsystem on the internal highway IH08-IH715 in two bytes using IUSTB as a strobe signal and H/L as the
byte indicator (high byte first followed by low byte). Data is valid about both edges of IUSTB. Signal timing for
this handshaking is shown in Figure 12.
If the subsystem does not declare itself busy, then it must respond to DTRQ going low by setting DTAK low
within approximately 1.5 us. Failure to do so will be classed by the RT as a subsystem failure and reported as
such to the Bus Controller.
It should be noted that IUSTB is also used for internal working in the RT. DTRQ being low should be used as an
enable for clocking data to the subsystem with IUSTB.
Once the receive data block has finished and been checked by the RT, GBR is pulsed low if the block is entirely
correct and valid. This is used by the subsystem as permission to make use of the data block. If no GBR signal
is generated, then an error has been detected by the RT and the entire data block is invalid and no data words in
it may be used.
If the RT is receiving data in an RT to RT transfer, the data handshaking signals will operate in an identical
fashion but there will be a delay of approx 70 µs between NBGT going low and DTRQ first going low. See
Figure 10.
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SCDCT1990 REV B 8/21/00 Plainview NY (516) 694-6700
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