Specifications

Chapter 1 – Introduction
Multi-Tech Systems, Inc. AT Commands for EDGE (E1) Modems (S000474A) 11
Several problems resulting from the use of GSM alphabet with ASCII terminal equipment:
• “@” character with GSM alphabet value 0 is not printable by an ASCII terminal program (e.g., Microsoft©
HyperTerminal®).
• “@” character with GSM alphabet value 0 will terminate any C string! This is because the 0 is defined as C
string end tag. Therefore, the GSM Null character may cause problems on application level when using a
‘C’- function as “strlen()”. This can be avoided if it is represented by an escape sequence as shown in the
table below.
By the way, this may be the reason why even network providers often replace “@”with “@=*” in their SIM
application.
• Other characters of the GSM alphabet are misinterpreted by an ASCII terminal program. For example, GSM
“ö” (as in “Börse”) is assumed to be “|” in ASCII, thus resulting in “B|rse”. This is because both alphabets
mean different characters with values hex. 7C or 00 and so on.
• In addition, decimal 17 and 19 which are used as XON/XOFF control characters when software flow control
is activated, are interpreted as normal characters in the GSM alphabet.
When you write characters differently coded in ASCII and GSM (e.g., Ä, Ö, Ü), you need to enter escape
sequences. Such a character is translated into the corresponding GSM character value and, when output later,
the GSM character value can be presented. Any ASCII terminal then will show wrong responses.
Examples for character definitions depending on alphabet
GSM 03.38
character
GSM character
hex. value
Corresponding
ASCII character
ASCII Esc
sequence
Hex Esc
sequence
Ö 5C \ \5C 5C 35 43
“ 22 “ \22 5C 32 32
@ 00 NULL \00 5C 30 30
Caution: Some terminal programs do not recognize escape sequences, and thus, handle escape sequences as
normal characters. Ways of writing escape sequences depend on the used terminal program.
To prevent misinterpretation of control characters or special characters it is recommended to prefer the USC2
alphabet and/or PDU mode in any external application
.