CDR-3250/80 TECHNICAL MANUAL
3-48 Issue 2.2
3-8.3.2.2 Serial Bus Interface Status Messages. Interface
status messages contain error status information caused by
a previous command message or other source. When the
receiver is in the acknowledge mode, it will respond to all
command messages (except X and V) with an interface
status message unless the command explicitly requested a
status message.
3-8.4 Serial Bus Message Protocol. The interface
system operates in one of three modes: normal, ac-
knowledge, or independent. These modes are selected by
sending the receiver the appropriate interface command
message. Each of the three modes are discussed in the
following paragraphs:
3-8.4.1 Serial Bus Normal Mode. In Normal Mode the
receiver unit will process messages that are addressed to it
but no response will be sent back unless the Command
Message was a request for Status Message (Radio or Inter-
face). The controller can verify that its Command
Message(s) was received without error by sending a
Command Message requesting a reply Status Message
either immediately after sending the original Command
Message, or after having sent Command Messages to other
receiver units. This mode allows the fastest throughput of
commands to a large group of receivers because the
controller does not have to wait for each receiver unit to
process the message(s) before moving on to the next
receiver unit.
3-8.4.2 Serial Bus Acknowledge Mode. In Acknowledge
Mode a receiver unit will always respond to Command
Messages with a Status Message after it has processed the
Command Message (except for the X and V commands). If
the Command Message was for a reply Radio Status
Message, and no errors or faults have been detected, the
reply will be the requested Status Message. In all other
cases, the receiver unit will respond with an Interface
Status Message. This mode reduces maximum throughput
because the controller must wait for the reply Status
Message before issuing another command, but it simplifies
the controller's job when it wants to verify the reception of
its Command Messages and maximum throughput is not
needed.
3-8.4.3 Serial Bus Independent Mode. In Independent
Mode the receiver will send a specific Status Message
whenever a squelch break occurs. This will occur
independently of any Command Messages. Independent
Mode is intended to be used only in non-controller
systems with a terminal or printer unless the controller
implements a method of handling contention. Three sub
modes are available: Independent Mode 1 which causes a
frequency and channel number report (F? and CN?) to be
sent, Independent Mode 2 which causes a complete status
message (R?) to be sent, and Independent Mode 3 which
causes a signal strength report (SS?) to be sent. These
modes can be used to keep a printed record of signals
detected during sweep or scan operation.
3-8.5 Line Driver Operation. When Bus Sharing is
enabled through the receiver's front panel, that receiver's
Transmitted Data and Request to Send line drivers are
maintained in a high impedance state at all times except
when it is required for that unit to transmit. In Normal Mode
operation, this only occurs when the unit has received a
Command Message that requests a reply Status Message.
In Acknowledge Mode, all commands will caused the
addressed unit to transmit.
The line drivers will be turned on and placed into the mark
state for at least one full character time before the first
character (the STX) is transmitted.
3-8.6 Broadcast Address. All receivers equipped with
the serial interface will respond to address 255 the same as
its actual configured address. This is referred to as the
broadcast address. If a single transmission is sent to this
address, each receiver on the bus will respond to the
commands in the transmission as if they were sent to it
individually. This feature may be used to cause a group of
receivers to act in unison, or to reduce the time it takes to
initialize a group of receivers to a set of common
parameters.
The broadcast address must not be used to request status
from a group of receivers or when the receivers are
operating in the acknowledge mode, since this would cause
bus contention as all receivers would reply at the same
time. With only one receiver on the bus it is possible for
the controller to determine the unit's address by sending a
status request to the broadcast address and examining the
address field in the reply, since the reply message contains
the unit's configured address. This can be used during
system integration as a troubleshooting aid.
3-8.7 Serial Bus Message Definition. All messages are
ASCII encoded and inserted into the data field of
transmissions as defined in paragraph 3-8.2. Messages
from the controller may use lower or upper case for all
alphabetic characters. The receiver always uses upper
case.
Each message that can be sent using the bus controller is
listed in the following tables:
o Table 3-3. Serial Bus Interface Command Messages.
o Table 3-4. Serial Bus Interface Status Messages.
o Table 3-5. Radio Command and Status Messages
Courtesy of http://BlackRadios.terryo.org
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