User's Manual

any modem with a unit ID 1200 through 12FF. Sending data with a
destination ID of FF34 will be received by any modem with a unit ID of 0034
through FF34.
The Address Mask
The reason to use hexadecimal digits to represent the unit address, is that
along with the Unit Address programmed into the FireLine, there is an
“Address Mask” programmed into it. The default mask is FFFF. The address
mask is also used to determine if a particular data transmission should be
received by the modem. For most applications, where one modem talks to
one modem, or where all modems in the system communicate with all other
modems in the system, the Address Mask should stay set to FFFF.
Only in systems where some modems should only talk to certain other
modems, might you want to change the address mask. Whenever data is
received over the air, the Destination Address of the transmission is logically
“ANDed” with the Address Mask in the receiving modem. This is the Effective
Destination Address. The receiving FireLine also ANDs its own Unit Address
with its Address Mask. The result is the Effective Unit Address. The Effective
Unit Address is compared to the Effective Destination Address, and if the two
are identical, the data will be received.
Note: Logically 1 AND 1 = 1, 0 AND 0 = 0, 1 AND 0 = 0, 0 AND 1 = 0
` Figure 2 (Address Filtering)
One effect of this is that an address mask of 0000 will cause the FireLine
modem to received any data from any unit that transmits. The Destination
Address will effectively be ignored if the mask is set to 0000.
FireLine receives
data over-the-air to
Destination Address
xxxx
FireLine has
Unit Address
yyyy
FireLine has
Address Mask
zzzz
“
AND
” them
together
Compare the two
results from these
two ANDs
“AND”
them
together
Output t
he data via
serial port if the two
results were
identical