Publication 1747-RM001G-EN-P - November 2008
13-76 SLC Communication Channels
DF1 Radio Modem
Communications
Processors running OS Series C FRN 6 and higher firmware include a new
channel 0 system mode driver called DF1 Radio Modem. This driver
implements a protocol, optimized for use with radio modem networks, that is
a hybrid between DF1 Full-duplex protocol and DF1 Half-duplex protocol,
and therefore is not compatible with either of these protocols.
Like DF1 Full-duplex protocol, DF1 Radio Modem allows any node to initiate
to any other node at any time (if the radio modem network supports
full-duplex data port buffering and radio transmission collision avoidance).
Like DF1 Half-duplex protocol, a node ignores any packets received that have
a destination address other than its own, with the exception of broadcast
packets, store and forward packets, and passthru packets (see Chapter 14 for
more information about channel-to-channel passthru capabilities).
Unlike either DF1 Full-duplex or DF1 Half-duplex protocols, DF1 Radio
Modem protocol does not include ACKs, NAKs, ENQs, or poll packets. Data
integrity is ensured by the BCC or CRC (recommended) checksum.
The primary advantage of using DF1 Radio Modem protocol for radio modem
networks is in transmission efficiency. Each read/write transaction (command
and reply) requires only one transmission by the initiator (to send the
command) and one transmission by the responder (to return the reply). This
minimizes the number of times the radios need to key-up to transmit, which
maximizes radio life and minimizes radio power consumption. In contrast,
DF1 Half-duplex protocol requires five transmissions for the DF1 Master to
complete a read/write transaction with a DF1 Slave - three by the master and
two by the slave.
The DF1 Radio Modem driver can be used in a pseudo Master/Slave mode
with any radio modems, as long as the designated Master node is the only node
initiating MSG instructions, and as long as only one MSG instruction is
triggered at a time.
IMPORTANT
The DF1 Radio Modem driver should only be used among
devices that support and are configured for the DF1 Radio
Modem protocol.
IMPORTANT
There are some radio modem network configurations that
will not work with the DF1 Radio Modem driver. (See DF1
Radio Modem System Limitations on page 13-77.) In these
configurations, continue to use DF1 Half-duplex protocol.
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