Specifications
Chapter 1 – Introduction
Multi-Tech Systems, Inc. AT Commands for EDGE (E1) Modems (S000474A) 10
1.5 Communication between Customer Application and
the MTSMC-E and E1
Leaving hardware flow control unconsidered the Customer Application (TE) is coupled with the MC75i (ME) via
a receive and a transmit line.
Since both lines are driven by independent devices collisions may (and will) happen. For example, if the TE
issues an AT command the MC75i starts sending a URC. This will probably cause the TE to misinterpret the
URC being part of the AT command's response. To avoid this conflict the following measures must be taken:
• If an AT command is finished (with "OK" or "ERROR") the TE shall always wait at least 100 ms before
sending the next one. This applies to bit rates of 9600 bps or higher (see AT+IPR). At bit rates below
9600 bp the delay must be longer: 300 ms at 1200 bps, and 500 ms at 300 bps.
The pause between two AT commands gives the MC75i the opportunity to the transmission of
pending URCs and get necessary service.
Note that some AT commands may require more delay after "OK" or "ERROR" response, refer to the
following command specifications for details.
• The TE shall communicate with the MC75i using activated echo (ATE1), i.e. the MC75i echoes
characters received from the TE.
Hence, when the TE receives the echo of the first character "A" of the AT command just sent by itself
it has control both over the receive and the transmit paths.
Using Backspace at command line:
• As the standard GSM alphabet does not provide a backspace functionality the MC75i is designed to
use the character "08" (hex 0x08) as backspace for command line input. This allows the user to easily
erase the last character when writing an AT command. On the other hand, this solution requires
entering the escape sequence \08 for writing the "ò" character in GSM character string parameters.
Software flow control:
• • Regardless of the selected alphabet, keep in mind that, when software flow control is activated,
decimal 17 and 19 are interpreted as XON/XOFF control characters.
1.6 Supported Character Sets
The ME supports two character sets: GSM 03.38 (7 bit, also referred to as GSM alphabet or SMS alphabet) and
UCS2 (16 bit, refer to ISO/IEC 10646). See AT+CSCS for information about selecting the character set. Character
tables can be found below.
Explanation of terms
• International Reference Alphabet (IRA)
IRA means that one byte is displayed as two characters in hexadecimal format. For example, the byte 0x36
(decimal 54) is displayed as “36” (two characters). IRA is used here for input 8-bit or 16-bit data via terminal
devices using text mode. This means only characters ‘A’..F’,’a’..’f’ and ‘0’..’9’ are valid.
• Escape sequences
The escape sequence used within a text coded in the GSM default alphabet (0x1B) must be correctly
interpreted by the TE, both for character input and output. To the module, an escape sequence appears like
any other byte received or sent.
• Terminal Adapter (TA)
TA is used equivalent to Mobile Equipment (ME) which stands for the GSM module described here. It uses
GSM default alphabet as its character set.
• Terminal Equipment (TE)
TE is the device connected to the TA via serial interface. In most cases TE is an ANSI/ASCII terminal that
does not fully support the GSM default alphabet, for example MS HyperTerminal.
• TE Character Set
The character set currently used by Terminal Equipment is selected with AT+CSCS.
• Data Coding Scheme (dcs)
DCS is part of a short message and is saved on the SIM. When writing a short message to the SIM in text
mode, the dcs stored with AT+CSMP is used and determines the coded character set.