Raveon RV-M8S Technical Manual - page 23
Company Confidential
23
Raveon Technologies Corp.
In Packet Mode, selection of the serial port baud-rate is important. As shown
above, if the serial port baud-rate is the same as the over-the-air baud rate and
the packets are short, the channel utilization is only about 50%. But, if the serial
port baud rate is set much higher, say 2-8X the over-the air rate, the channel
utilization becomes near 100%.
Because the M8S can handle serial-port data rate far in excess of the over-the-
air rate, the efficiency of the M8S in Packet Mode is approximately the same as
other brand modems that cannot operate in a Packet Mode
— with the added
benefit or ARQ, error-free data, and addressing.
Busy-Channel Lock Out
If your system operation require the M8S modem to monitor-before-transmit, of if
you do not want the M8S 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 M8S 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.
7.4. Addressing (Packetized Mode only)
Addressing Basics
One of the more powerful aspects of the
M8S
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
M8S
contains a 16 bit address, called its Unit Address, and is represented
as a 4 digit hexadecimal number.
M8S
address may be any number between
0000 and FFFF, which is effectively 65,535 different addresses. Every
M8S
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.
The defaults UNIT ID in al
M8S
modems is 1234, and 1234 is the default for the
destination ID. An Address Mask is used to select which digits of the address will
be used to determine if a particular reception was intended for the M8S modem.
The default Address Mask is FFFF, which means all digits will be used. With