User's Manual

Company Confidential 17 Raveon Technologies
If the channel number is changed using the ATHP command, and power is
later lost, the channel number will be retained in non-volatile memory as long
as was saved using the ATSV (Save to non-volatile memory) command.
Due to the nature of the synthesizer used in the M7-UC’s radio, the frequency
programmed into the unit must be an even multiple of its internal reference
frequency. For narrow-band radios (12.5kHz channels), the user’s frequency
must be a multiple of either 6.25khz or 5.00kHz. For wide-band models, the
frequency must be an even multiple of 10kHz or 12.5kHz.
6.3 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-UC. Because the buffers in the M7-UC 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-UC can handle serial-port data rate far in excess of the over-
the-air rate, the efficiency of the M7-UC 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-UC, 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 1 command. Note that the M7-UC modem will
always indicate the status of its internal buffer using the CTS signal on the
DB-9 serial connector. When CTS is negated, the internal buffers are more