Company Confidential
16
Raveon Technologies Corp.
9.7 Key-On_Data
When serial data is entering the
Radio Modem
’s RS-232 port, the
Radio Modem
looks for pauses in the data as indication that it is time to send a packet of data
over the air. The factory default duration of the pause it looks for is 20mS, but
the user may change this to other values using the
ATR3 xxx
command, where
xxx is in milliseconds.
9.8 Busy-Channel Lock Out
If your system operation requires the modem to monitor-before-transmit, or if you
do not want the Radio Modem to transmit on a channel that is busy, you can
enable “Busy-Channel-Lockout”, using the
ATBC 1
command.
ATBC 0
disables
BCL, and thus the modem will transmit whenever it has data to send out. The
factory-default is BCL disabled. Use caution when enabling it, as a CW
interferer, PC with poor shielding, or some other source of RF can stop the
modem from transmitting. The threshold where the Radio Modem senses RF
carrier, and determines that the channel is busy is set by the
ATRA
command.
This is factory calibrated to an equivalent RF level of approximately -110dBm.
9.9 Data Reception
When the modem receives data over the radio, it checks it for errors, and if it is
error-free, it will send it out the serial port. Again, the serial port may be set to
any baud rate the user wishes, and the radio receiver and transmitter will
continue to operate independently of the baud rate.
When the modem receives a signal, it will assert the CD hardware signal on the
RS-232 serial port if it was configured to do so.
9.10 Addressing (Packetized Mode only)
9.10.1 Addressing Basics
One of the more powerful aspects of the modem is its addressing scheme.
Incorporating addressing in the modem allows multiple radio systems on the
same frequency to co-exist, and not interfere with each other. Also, some user
application cannot tolerate receiving data that was not intended for it, and by
setting the addresses in the modems properly, the system can be configured to
allow reception of only data intended for the recipient.
If addressing is not needed or desired, it can be turned off so that all modems
receive data from all other modems, and all modems can talk to all other
modems.
Each
Radio Modem
contains a 16 bit address, called its Unit Address, and is
represented as a 4 digit hexadecimal number.
Modem
address may be any
number between 0000 and FFFF, which is effectively 65,535 different addresses.
Every modem has a Unit Address programmed into it, as well as the ID of the
unit it will send data to. The Unit Address is programmed with the
ATMY xxxx
command, and the Unit Address of the destination modem (the Destination
Address) is configured with the
ATDT xxxx
command.
