Campbell Scientific RF300-Series DRL VHF/UHF Radio Transceivers - Manual (Page 23)

SECTION 3. RADIOTELEMETRY NETWORK COMPONENTS
3-5
occurs between characters, the data block will
be closed and transmitted.
Most of the time, the SOL modem will be
sending command strings which will be
answered by the EOL modem and the
datalogger. The response from the datalogger
is not instantaneous. If a command is sent
before the response from the previous
command has been received, the current
command will be sent and a possible collision of
the RF signal may occur. This results in a loss
of the response and the current command. The
general rule is that the person sending
characters should wait for the response to come
back before issuing further commands.
3.1.7.3 Shutting Down the RF Link
Sending the "E" character to a datalogger
causes the datalogger to drop its ME line, which
causes a shutdown of the RF link.
A shutdown block is created by the EOL
modem which can be sent to the computer as
an indicator of communication quality. The
shutdown block consists of three RF Link
Quality Accumulators (RLQA). Each RF95A in
the link will have three RLQAs which are
appended to the shutdown block. The RLQA
from each RF95A are representative of the
active period of the link. The first three RLQAs
represent the EOL modem connected to the
datalogger, the following sets of numbers will be
for any MOL modems (in order of occurrence
from the EOL modem), and last will be the SOL
modem. A description of the shutdown block is
contained in Table 3-3.
TABLE 3-3. Summary of the Shutdown
Block
xxxx yyyy zzzz
xxxx = Number of
communication failures.
yyyy = Noise level indicator.
zzzz = Noise level indicator.
A communication failure occurs when a
signature of a block of data doesn't match its
original signature. These blocks are
subsequently retransmitted. The noise level
indicators should be 102 (
± 70) at the standard
3.0K baud rate, or 124 ( ± 70) at 2.4K baud.
The noise level indicators are reset and
subsequently become active in the respective
EOL and SOL modems as the Transparent
Mode is entered (immediately after setup). The
MOL modems are reset and become active
when the setup block is propagated to the next
station in the RF link.
After the "E" character is received by the
datalogger a CR-LF is sent through the RF link
to the SOL modem. The shutdown block
follows after a one second delay. When the
shutdown block is received and verified the SOL
modem will leave the Transparent Mode and re-
enter the Local Command Mode, indicated by
sending an exclamation point (!) to the
computer.
The shutdown block can be viewed by sending
the "R" command. Example 3-2 illustrates a
shutdown block for three RF95s.
EXAMPLE 3-2. Sample Shutdown Block
!R
EOL modem - > 0004 0110 0097
MOL modem - > 0002 0108 0090
SOL modem - > 0000 0105 0093
!
The first line of numbers, which are the first
three RLQAs, represent the EOL modem. The
second line represents a MOL modem, and last
is the RLQAs for the SOL modem. The 0004
indicates that four interruptions occurred on the
EOL modem while the link was active.
Interruptions are non-data blocks such as voice
transmissions on the same carrier frequency.
All noise level indicators are within acceptable
bounds in this example.
The "T" command should now be used to reset
the SOL modem to the Wait Mode of operation.
This step should not be done if further calls are
going to be made through a phone modem.
3.1.8 RF95A CONNECTIONS
The 9-pin Serial I/O connector is normally used
to connect the RF95/A to the datalogger,
PS512M or CH512R. Table 3-4 describes the
9-pin connections. The 10-pin rectangular
connector is for connection to the transceiver.
The RF300 transceiver cable has a different pin
out then the RF100/200 transceiver cable.