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. Figures 29 and 30 show typical interfacing logic.
Figures 5 and 15 shows the operation of the data handshaking signals during a receive command with one
data word. 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 15. Also see Figures 19 and 20.
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
Aeroflex Circuit Technology
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SCD3492 REV B 6/26/01 Plainview NY (516) 694-6700
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