Multitech MultiModem Cell MTCBA-C1 User's Guide download pdf (Page 9)

Chapter 2 – AT Commands Overview

Multi-Tech Systems, Inc. CDMA C1 AT Commands Reference Guide (PN S000478C) 9

Command Types

Terminology Used to Describe AT Command Communication

Term Definition

AT Command

This is referred to as a command from the host application to modem with a

request to perform a service.

Result Code

This is an immediate response to a command, informing the host application

whether the execution of the command succeeded or failed. The strings “OK” or

“ERROR” are the only two Result Codes available. A result code is always

returned after an AT command has been sent to the modem.

Extended Reason Code

If enabled, (see AT+CMEE), modem responds with a detailed reason code string

in addition to “OK” or “ERROR”. The reason code is returned before the result

code. Extended reason codes are only provided when the result code is ERROR.

Response

A response contains data that has been requested via an AT command. A

response is returned before the result code of the command. A response is

provided only when the result code is OK.

Unsolicited Response

An unsolicited response is sent by modem when a specific event occurs. Some

unsolicited responses can be turned on and off via AT commands. Some

unsolicited responses are always enabled or turned on.

Three Types of AT Commands

Command Type Definition

Action Command

Action commands are used to perform a function. Typically, action commands are used

to change the value of a setting in modem, send data, or perform advanced queries that

require input data.

Read Command

Read commands typically end with a “?”. Most read commands do not have any input

parameters; however, in some cases an input parameter provides options for the

response format. The read commands are used for reading values of certain settings in

the modem.

Test Command

Test commands are not supported in the C1 modem.

Command Format and Syntax

Alphabet

The T.50 International Alphabet 5 (IA5) is used in this manual. Only the low-order seven bits of each character

are significant to modem. Any eighth or higher-order bit(s) are ignored for the purpose of identifying commands

and parameters. Lower-case characters (IA5 values from 0x61 to 0x7A) are considered identical to their upper-

case equivalents (IA5 values from 0x41 to 0x5A) when received by modem from the host application. Result

codes from the modem shall be in upper case.

All commands must begin with the characters A and T. If the A and T are not received by the software, the

remaining characters will not be processed. This is important; should the A or T be lost in communication or not

supplied, none of the characters sent to the modem will be echoed back until an AT sequence is observed.

Command-Line Editing

The character defined by the command ATS5 in chapter 9.14, (default: backspace [IA5 0x08]) is intended to be

interpreted as a request from the host application to the modem to delete the previous character.

Any control characters (IA5 0x00 through 0x1F, inclusive) that remain in the command line after receipt of the

termination character are ignored by the modem.

Before checking for other characters, the modem checks characters from the host application to see if they match

the termination character (S3), then it checks to see if they match the editing character (S5). This ensures that

these characters will be properly recognized even if they are set to values that the modem uses for other

purposes. If S3 and S5 are set to the same value, a matching character will be treated as matching S3 (S3 is

checked before S5).

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