Specifications

RV-M7 Technical Manual

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 M7 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 M7 to ignore the address, and receive every transmission. The

disadvantage to this method is the adjacent-system problem. If there is another M7 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 M7 with a Unit Address of 0001, 0002, 0003, etc… Set

the address Mask to F000. This will let all M7s 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 M7’s and the units that have IDs starting with 0xxx will only hear other radios with

IDs that start with 0xxx.

Broadcast Transmissions

The double FF is used to identify a broadcast packet. A transmission with 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 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 M7, there is an “Address Mask” programmed into it. The default

mask is FFFF. The address mask is 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 M7 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