Campbell Scientific RF300-Series DRL VHF/UHF Radio Transceivers - Manual (Page 47)

E-1
APPENDIX E. RF95A STATES
The RF95A Modem operates in one of two
separate states. The RF95A can be utilized in
either the RF95A-ME (Modem Enable) State or
the RF95A-SDC (Synchronous Device
Communication) State. The RF95A-ME State is
normally used for all RF networks. The RF95A-
SDC State must be used when there is a
phone-to-RF base station with a datalogger.
Note: the 21X and CR7 dataloggers don’t
support the SDC state. A switch inside the
RF95A needs to be set according to the chosen
state.
E.1 RF95A-ME STATE
The RF95A-ME State is always used with 21X
and CR7 dataloggers, and normally with all
other dataloggers.
RF95A-ME State Description
The RF95A rings the datalogger until the
datalogger raises the ME line. The Datalogger
waits approximately 40 seconds to receive
carriage returns to establish the baud rate.
After the baud rate is set the Datalogger
transmits a carriage return, line feed, "*", and
enters the Telecommunications Mode. If the
carriage returns are not received within the 40
seconds, the Datalogger hangs up.
When the datalogger is in the
Telecommunications Mode, the ME line is high,
and the RF95A is subsequently in the
Transparent Mode or EOL Mode depending on
the relative location of the RF95A.
E.2 RF95A-SDC STATE
The RF95A-SDC State can be used to enable a
Datalogger to be recording measurements at a
phone-to-RF base station. The SDC State is
never used with 21X or CR7 dataloggers.
RF95A-SDC State Description
The RF95A obeys all Synchronous Device
Communication (SDC) protocol when set in the
RF95A-SDC State. Most dataloggers have the
ability to address synchronous devices. The
21X and CR7 do not support the SDC state.
The Datalogger and the RF95A use a
combination of the Ring (pin 3),
Clock/Handshake (pin 7), and Synchronous
Device Enable (SDE, pin 6) lines to establish
communication rather than just the Modem
Enable line.
When the Datalogger is connected to the
RF95A, a 1N command is sent to the
datalogger at setup. The baud rate is set and
the Datalogger completes connections with the
RF95A. The Datalogger sets the RF95A in an
addressing state by raising the CLK/HS followed
by or simultaneously raising the SDE line. The
RF95A drops the ring line and prepares for
addressing.
The Dataloggger then synchronously clocks 8
bits (the address) onto TXD using CLK/HS as a
clock. The least significant bit is transmitted
first, each bit is transmitted on the rising edge of
CLK/HS. The RF95A completes addressing
when the eighth bit is received.
The synchronous device capability enables the
Datalogger to have measurement capability at a
phone-to-RF base station. A command within
the address sent to the RF95A can tell the
RF95A to connect to the phone modem which
requires the RF95A to switch its TXD and RXD
lines. Therefore all characters are routed
through the phone modem to the RF95A which
controls the radio accordingly.
The RF95A then enters the Active State. The
receiver is enabled when SDE and CLK/HS are
high. The transmitter is enabled when SDE is
high and CLK/HS is low.
In the Active State, the RF95A responds to the
commands S, R, T, F, and U.