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MFJ-1278B MULTI-MODE ADVANCED OPERATION
Commands Affecting Protocol
This section describes some of the commands that affect the operation of the packet protocol.
Details of the protocol are given in Chapter 9.
The MFJ-1278B implements AX.25 Level 2 protocol, a set of rules for formatting messages
to other TNCs. The version of AX.25 Level 2 protocol used by the MFJ-1278B can be set to
Version 2.0 with the command AX25L2V2 ON, or to Version 1.0 with the command
AX25L2V2 OFF. Digipeating may not be successful if some MFJ-1278Bs are running
Version 1.0 and some are running Version 2.0. In addition, the command CHECK controls
a timing function that depends on the protocol version selected.
You can specify the "address" to be used for unconnected packets, as well as intermediate
digipeaters with the UNPROTO command. The format is similar to that of the CONNECT
command:
cmd: UNPROTO QST VIA NK6K
The default address for unconnected packets is CQ.
The following functions may be useful for tracking down protocol problems. They are
seldom useful for ordinary packet operations. The PASSALL command disables the error-
checking function of the packet protocol for monitored packets.
The MFJ-1278B will display any packets if they meet the following conditions, if the
PASSALL command is ON:
1. It must start with a flag sequence; and it must contain an integral number of 8-bit bytes.
2. The TRACE command enables the display of the address and control fields of packets,
as well as the text. The trace function displays all bytes in hex as well as ASCII
equivalents.
Packet Timing Functions
Transmit Timing
Amateur radio equipment varies greatly in the time delays required in switching from receive
to transmit and from transmit to receive. If the MFJ-1278B starts sending data before the
transmitter is operating or before the receiver has had time to switch from transmitting and
lock up on the incoming signal, the packet will not be received properly. The delay between
transmitter keyup and the beginning of data transmission is controlled by the command
TXDELAY
. During the time the MFJ
-
1278B is keying the transmitter but not sending data,