Specifications

RV-M7 Technical Manual

6. Using the M7 Modem – Packet Mode

This section describes the operation of the when it is in the Packet Mode of operation. Packet Mode

is the factory-default operating mode. It is the easiest and most reliable mode of operation for a

modem. Note: The configuration of the M7 is done when the M7 is in the “Command Mode”.

Refer to Section 5. on page 18 for details on all of the available commands and programmable

features.

In Packet Mode, all transmissions are sent in bursts or packets, and contain address, error

detection, and error correction information. Date enters the M7 modem’s serial I/O port, and is

stored in a buffer within the modem until it is ready to be transmitted. Packetized operation

has these advantages over non-packet modems:

Packet Mode Advantages

1. Error Detection The modem uses a 16-bit CRC at the end of every packet of data. The CRC

is used to check the data for errors, and if there are any errors, the data will not be passed

onto the user.

2. Error Correction Automatic error correction may be used. M7 modems incorporate an

optional ARQ method to re-transmit packets with error, to ensure the user’s data is

delivered error-free.

3. Addressing Packetized operation allows for a more versatile network architecture, with

source, destination, and network addresses. M7 uses a 16-bit address to identify data

packets.

4. No Dribble Data Even in the presence of noise, the M7 modem will not output extra data or

have random bit errors. Modems without packet operation generally do not work well with

weak noisy signals.

5. Transparent Operation Because of the high-reliability and error-free operation the Packet

Mode offers the user, most user applications will seamlessly work using the M7 in its Packet

Mode.

6. Repeatable and Routable. M7 packets are structured so that they may be repeated using a

store-and-forward repeater, and/or routed using specialized hardware.

Streaming Mode Advantages

1. Low Latency The transmitter will key-up immediately upon the user’s first byte of data

entering the modem. Packetized operation waits until a packet has been loaded before

keying. (Although high serial-port data rates can minimize this packet latency to a negligible

level).

2. Data with Errors The M7 will continue to receive data, down into the noise-floor of the

radio. If the channel is noisy or the signal is weak, there may be bit-errors in the data, or the

M7 may output additional noise data. User applications must (and often do), take this into

account, and thus can operate with weaker signals and have longer communication range.