RV-M7 Technical Manual
The factory default condition is not to send or require ACK packets, so if you wish to use this mode,
program the M7 to transmit ACKs with the ATAK 1 command. This will cause the modem to send
an ACK anytime it receives data from another modem. Note: If the destination address was a
broadcast (FFFF, FFxx, or xxFF), it will not wait for an ACK.
The number of times it retries to send data that does not get through (does not get an ACK) is up to
the user, but a number of 5 is usually a good compromise. If after 5 times, the data does not get
through, then there probably is something seriously wrong with the channel or system.
The retried-transmissions are randomly spaced at intervals between approximately 200mS and
400mS, increasing by 50mS for each attempted transmission. Once the modem has sent its data the
number of times the user specified in the ATRB xx command, the data is discarded, and the modem
will continue to operate as normal.
It is very important that if one modem is configured to send ACK packets (ATAK 1) that all other
modems communicating with it are also set to expect ACK packets using the ATRB xx command.
To disable ARQ (the default condition of the modem), disable ARQ with the ATAK 0 and set retries
to zero with the ATRB 0 command.
6.6 Store-and-Forward Repeating
The M7 modem has a built-in wireless repeater. Each M7 is capable of not only sending and
receiving data from/to its serial port, but also re-transmitting data packets it receives over-the-air
data.
Automatic Repeater Configuration
The easiest way to enable store-and-forward repeating is the use the REPEAT 1 command. REPEAT 1
will turn on the store-and-forward feature, and configure it to repeat all packets the radio can hear
on the air. REPEAT 0 disables store-and-forward repeating.
It is highly recommended that you use this method to configure your M7 as a repeater.
Important: The Unit ID of the repeater must be unique in the system. No other radio modem in the
system can have the ID of the repeater.
Manual Configuration of the Repeat Feature
There is a sophisticated packet repeating algorithm in the M7, and it may be manually configured for
more complex repeating scenarios. In most cases this is not needed. Simply use the REPEAT 1
command. But, if you do not wish the repeater to repeat all packets, you may manually configure
the Repeater Table within the M7. The Repeater Table is a table of IDs that the M7 should repeat. It
contains a range of IDs and a mask. There may be up to 4 entries in the Repeater Table, each with a
different range of IDs that should be repeated.
Important: The Unit ID of the repeater must be unique in the system. No other radio modem in the
system can have the ID of the repeater.
Data is transmitted over-the-air in bursts called packets, and each packet has the Unit ID of the M7
that sent the data and the Destination ID of the unit that the data is intended for.
(10 pages)
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