User's Manual

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, FireLine 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 FireLine 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 FireLine to ignore the address,
and receive every transmission. The disadvantage to this method is the
adjacent-system problem. If there is another FireLine 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.
Broadcast Transmissions
The double FF is used to identify a broadcast packet. A transmission with a
two digit FF in the first two positions of the destination ID, or in the last two
positions of the destination ID, will be interpreted as a broadcast, and any
modem with an ID that matches the two non-FF digits will receive the data.
For example, sending data with a destination ID of 12FF will be received by