Company Confidential
17
Raveon Technologies Corp.
The default UNIT ID in all
Radio 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 modem. The
default Address Mask is FFFF, which means all digits will be used.
9.10.2 Hexadecimal Numbers
For those not familiar with hexadecimal numbers, a hexadecimal digit represents
a 4-bit binary pattern. There are 16 possible values
(0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,and F). These 16 values represent 4 bits of
information, thus 4 hexadecimal digits can represent 16 bits of information. The
hexadecimal numbers represent 4 bit data in the following way:
Hexadecimal Table
Hex #
Binary
Hex #
Binary
Hex #
Binary
Hex #
Binary
0
0000
5
0100
8
1000
C
1100
1
0001
6
0101
9
1001
D
1101
2
0010
7
0110
A
1010
E
1110
3
0011
8
0111
B
1011
F
1111
When communicating over the air, the radio modems transmit their Unit Address
and the Destination Address along with the data. Receiving modems check the
received Destination Address, and see if it matches their Unit Address. If it does
match, the receiving modem outputs the data it received via its serial port. If it
does not match, the receiving modem discards the data, and does not send it out
the serial port.
9.10.3 Setting A System-Wide Address
If individual addressing is not needed in your system, there are two ways to
ensure it is not used. One way is to set all modems in the system with the same
Unit Address and destination address. From the factory, these are both set to
1234, and thus, all modems can communicate with all other modems, using the
address 1234. The advantage of using this system-wide address, is that if there
are other modems on the channel, but in some other system, they probably will
not have the same Unit Address, and thus will not interfere with your system. To
reduce the possibility of data cross-talk, the system implementer may wish to use
a different system-wide address for the Unit Address instead of 1234. There are
over 65,000 addresses available.
An alternate way to disable addressing altogether, is set the Address Mask to
0000 (
ATMK
0000 command). This tells the Radio Modem to ignore the
address, and receive every transmission. The disadvantage to this method is the
adjacent-system problem. If there is another Radio Modem system on the same
channel, all modems with the 0000 mask will receive them also.
Most users who do not use individual modem addressing, choose to set a global
system address, and have all modems in their system use the same Unit ID and
same destination address.
