Address, and see if it matches their address. If it does match, the receiving
mdoem 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.
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, will you want to change the address mask. Whenever data is
received over the air, the Unit Address of the device that sent the data is
logically “ANDed” with the Address Mask in the receiving modem. This is the
Effective Transmission 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 Transmission
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
`
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 Unit Address
will effectively be ignores if the mask is set to 0000.
FireLine receives
data over-the-air
from Unit 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 the data via
serial port if the two
results were
identical