Velocity Edge GX440 Specifications download pdf (Page 19)

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

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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Velocity Edge GX440 Specifications Page 19

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