User's Manual

Company Confidential 60 Raveon Technologies Corp.
5.2. Programming Channels
The M7 modem has memory for up to 6 channels. A channel is a pair of
frequencies, one for transmit and one for receive. They may be different or they
may be the same. You may program any valid frequency into any channel
number. To program a channel, perform the following steps.
1. Change to the channel you wish to program, using the ATHP x command,
where x is the channel number.
2. Review the frequency setting with the ATF command.
3. To change the radio channel, use the ATHP x command while the modem is
in the command mode.
5.3. Data Transmission
To transmit data, send one or more bytes of data into the serial port of the
modem. When a full packet of data has been collected into the internal buffer of
the modem, or when there is a pause in the data, the modem will automatically
key its transmitter, and send the data over the air.
Serial Port Baud Rate
While the modem is transmitting, the user may continue to send more data into
the M7. Because the buffers in the M7 are full-duplex, the serial port data rate
and the over-the-air data rates are independent. The serial port baud-rates may
be set slow to accommodate legacy equipment, or set at high-speed to minimize
latency. The over-the-air data rate us usually 4800 baud for narrow-band
channels, and 9600 baud for wide-band, although faster or slower rates may be
used.
In Packet Mode, selection of the serial port baud-rate is important. As shown
above, if the serial port baud-rate is the same as the over-the-air baud rate and
the packets are short, the channel utilization is only about 50%. But, if the serial
port baud rate is set much higher, say 2-8X the over-the air rate, the channel
utilization becomes near 100%.
Because the M7 can handle serial-port data rate far in excess of the over-the-air
rate, the efficiency of the M7 in Packet Mode is approximately the same as other
brand modems that cannot operate in a Packet Mode — with the added benefit
or ARQ, error-free data, and addressing.
Note that many Windows applications which use the serial port, such as
HyperTerminal, put large gaps between the bytes of data they send out the serial
port. If an application is not getting the desired throughput, verify that it is not an
artifact of the Operating System or the computer.
Flow Control
If large amounts of data will be sent with the M7,
it may be possible to overflow
the internal data buffer. To ensure the transmit buffer does not overflow, enable
and use hardware flow control. Hardware flow control is enabled with the ATCH