CDR-3250/80 TECHNICAL MANUAL
3-68 Issue 2.2
3-9 REMOTE OPERATION USING
IEEE-488 BUS.
The receiver can be operated under remote control, using
an IEEE-488 bus, if the optional IEEE-488 Remote Interface
board and bus plate are installed. Select the remote mode
by pressing the front panel REM/LOC switch until
CTRL:REMOTE appears in the display. When REMOTE is
selected, the bus controller determines whether the receiver
is in the remote or local mode.
NOTE
The bus controller can command
the receiver to enter the local
mode. When the controller
commands the receiver to enter
the local mode, the front panel will
display CTRL:LOCAL.
3-9.1 IEEE-488 Bus Description. The IEEE-488
bus uses a party-line bus structure consisting of 16 signal
lines. (Refer to table 3-6.) Devices are connected in parallel
to the bus and information is passed in a byte serial/bit
parallel fashion. Refer to IEEE Std 488-1978 for a complete
description of the IEEE-488 bus.
The sixteen signal lines are divided into three major func-
tional groups: bus management lines, handshake lines, and
data lines. There are five bus management lines, three
handshake lines, and eight data lines. Data and message
transfer is asynchronous. Devices connected to the bus
may be talkers, listeners, or controller. Multiple controllers
may be connected to the bus but only one controller may
be in charge at a time. The controller dictates the role of
the other devices by setting the ATN (attention) line true
and sending the talk or listen addresses on the data lines.
While the ATN line is true, all devices must listen to the
data lines. When the ATN line is false, only devices that
have been addressed will actively send or receive data. All
others ignore the data lines.
Several listeners can be active simultaneously but only one
talker can be active at a time. Whenever a talk address is
put on the data lines (while the ATN is true), all other
talkers will automatically be unaddressed.
The bus management lines conduct an orderly flow of
information across the bus. The five bus management
signals are defined in table 3-6.
The three handshake lines coordinate the transfer of data
over the bus. Transfer is asynchronous and the transfer
rate automatically adjusts to the speed of the source and
acceptor. The transfer rate will be that of the slowest active
device. The three handshake lines are defined in table 3-7.
The eight bidirectional data lines (D1 - D8) transfer the data
bytes on the bus. The bus management signals determine
which device sends and which devices receive the byte.
The handshake lines determine how long the byte remains
on the bus.
One 24-pin, D-type ("Blue Ribbon") interface connector
provides parallel connection for the receiver. A maximum
of fifteen devices, including the bus controller, may be
connected to the bus. (Each CDR-3250/80 chassis is
counted as one device.) Each receiver must have a unique
address set on the front panel.
The receiver may act as a talker and a listener. The SRQ
function is selectable by means of a switch on the rear
panel. If the SRQ function is disabled, the receiver can not
request controller attention for communication. Two other
switches on the rear panel are used to select the
unaddressed talk only and listen only modes.
3-9.2 Device Capabilities. The interface capabilities
implemented in the receiver are listed in table 3-8.
3-9.3 Talking and Listening. Commands sent to the
receiver are prefixed with the appropriate Listen Address
message and then the message is sent in ASCII as detailed
in table 3-5. Following the transmission, " Unlisten"
message may be sent or another transmission may be sent
while the unit is still addressed. Each transmission must
end with CR (carriage return) character. In addition, the EOI
(End or Identify) line must be set true concurrently with
the CR. An example of the bus transaction necessary to
change the receive frequency to 12.345 MHz is as follows:
<Listen Address> F 1 2 3 4 5 0 0 0 <CR with EOI>
The unit's configured remote control address serves as
both its Talk Address and its Listen Address, and may
range from 0 to 30. Multiple receivers may be addressed as
listeners and will all accept message transmissions
simultaneously when so addressed.
If the message sent to a receiver is a request for status (all
messages that end with '?') the receiver will prepare a reply
message and wait to be addressed as a talker. If the receiver
does not receive its talk address within 5 seconds of the
request for status, it will indicate a fault and stop waiting.
If it receives the talk address within 5 seconds, it will
perform the source handshake with the controller until all
of the reply message has been sent. If the controller does
not perform the acceptor handshake within 1 second of
sending the talk address to the receiver, the receiver will
time out, indicate a fault, and stop and return to normal
operation. The receiver will assert the EOI line on the bus
concurrently with sending the CR at the end of the status
message. It is not recommended that request for status
messages be sent to multiple receivers simultaneously.
Courtesy of http://BlackRadios.terryo.org
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