Sierra Wireless MP 700 Series, Command Reference Manual

Page: 19 / 118

Modem Basics
• If there is an active PAD (Packet Assembler/Disassembler)
session and the PAD is configured to use TIES (Time
Independent Escape Sequence), the modem switches to
command state on receipt of “
AT+++
”. (The “AT” must be
in upper case.) The command !MPPADCONF (described
on page 52) is used to enable and disable TIES.
When the modem changes to command state, it will issue an
OK
result. This may be preceded by another result (such as
NO
CARRIER
) to indicate that the session was closed by an event
outside the modem. The modem returns to command state when
a session is closed.
Modem Buffers
Communication between the host and modem is buffered
based on the modem’s state.
Command buffer
When in command state, the modem buffers the input from
the host until a
<CR>
is entered. The buffered data can be
edited using the backspace
<BS>
. The modem (unless Echo is
enabled) echoes the sequence
<BS><space><BS>
for human
readability.
There is a limit of 200 characters to one command line,
including the
AT
prefix and the
<CR>
termination (i.e. 197
characters of useful command buffer). If the command buffer
length is exceeded the modem will continue to echo input
(which is not buffered) until the
<CR>
is received. When the
<CR>
is entered, the modem returns the
ERROR
result code
without executing any commands in the line. Once over the
limit, the
<BS>
will not bring you back under the limit; the
ERROR
code is still returned.
The command buffer is distinct from the data receive and
transmit buffers. The command buffer retains the contents of
the last issued command until the
AT
command prefix is
received for the next command. This allows repeating of the
last issued command by entering
A/
.
Data buffers
Data being transmitted or received is buffered in several ways
depending on the mode and nature of the connection. Some
caution must be taken when disconnecting to ensure that any
buffered data in the modem has been properly processed prior
to breaking the connection.
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