Company Confidential
21
Raveon Technologies Corp.
5. Using the M8S 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
M8S
is done when the
M8S
is in the “Command Mode”. Refer to Section 1
on page 12 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 M8
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.
M8
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. M8 uses a 16-
bit address to identify data packets.
4.
No Dribble Data
Even in the presence of noise, the M8 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 M8 in its Packet Mode.
6.
Repeatable and Routable.
M8 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 M8 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 M8 may output additional noise data. User
