Company Confidential
26
Raveon Technologies Corp.
from 1-255, then the group feature is enabled, and the group number will be the
group specified in the
ATGP
command. When enabled, the M8 will only
communicate with other M8s that have the same Group Number.
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,
M8
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.
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 M8 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 M8 to ignore the address, and
receive every transmission. The disadvantage to this method is the adjacent-
system problem. If there is another M8 system on the same channel, all
modems with the 0000 mask will receive them also.
A good idea is to start numbering all of your M8 with a Unit Address of 0001,
0002, 0003, etc… Set the address Mask to F000. This will let all M8s with ID’s
0001-0999 talk to each other. If you want a separate group, start numbering
them 1000, 1001, 1002, etc… Then the 1000 series group will only hear 1000
series M8
’s and the units that have IDs starting with 0xxx will only hear other
radios with IDs that start with 0xxx.
