Company Confidential
45
Raveon Technologies Corp.
this value, Carrier Detect is asserted. The pre-set RSSI value may be change
with the
ATCD
command.
Note: “Asserted” means low. “Negated” means high. The CD pin will sit at about
3.3V when CD is not asserted. A digital 1 (3.3V) on the CD pin is the standard
convention used to indicate no carrier detect. This allows the digital signals like
the CD pin to be connected to standard RS232 line driver circuits and operated
with the correct polarity.
Mode 0 - RF CD
On this line the modem indicates to the DTE that it has received a carrier from a
remote device. It will assert this signal any time there is a carrier detected. The
modem may be configured to assert this when an RF carrier is detected (any on-
channel RF, voice or data), assert it only when another RF modem signal is
detected, or always assert it. The operation of this line is configured with the
ATR1 command. The default is 1 (asserts when
M8
data is detected on the radio
receiver).
ATR1 1 Mode 1 - Data CD
In this mode, the CD pin is asserted whenever the modem detect a valid data
modem signal on the air. If RF is present, but it is voice or some non-data single,
then the CD pin is negated.
ATR1 2 Mode 2 - CD ON
In this mode, the CD pin is always asserted.
ATR1 3 Mode 3 - CD OFF
In this mode, the CD pin is always negated.
ATR1 4 Mode 4 - Output Data Framing
To enable the
Output Data Framing
feature, set
ATR1
to
4
, set
ATS120
to the
number of mS for the Pre-Data Time, and
ATS121
to the number of mS for the
Post-Data Time.
Output Data Framing is used when it is necessary for the serial terminal to wake
from sleep or enter an appropriate mode to receive data. In this mode, the
Carrier Detect handshaking line is nominally low and only goes high to signal that
data is being output. The Pre-Data and Post-Data time can be set from 0-254ms,
as indicated in the diagram below. The CD signal will normally stay low (near 0
volts), and when the Output Data Framing takes place, it will go high (about 3V).
