AT Command Set
MC35_ATC_01_V05.00 Page 17 of 256 15.07.2002
1.5 Supported character sets
The ME supports two character sets: GSM 03.38 (7 bit, also referred to as SMS alphabet) and UCS2
(16 bit, refer to ISO/IEC 10646). See Chapter 4.44 for information about selec ting the character set.
Character tables are provided in Chapter 9.5.
Due to the constraints described below it is recommended to prefer the USC2 alphabet in any external
application.
If the GSM alphabet is selected all characters sent over the serial line ar e in the range from 0 ... 127.
CAUTION: GSM alphabet is not ASCII alphabet!
Several problems resulting from the use of the GSM alphabet:
1. "@" character with GSM alphabet value 0 is not printable by an ASCII terminal program (e.g. Mi-
crosoft© Hyperterminal®).
2. "@" character with GSM alphabet value of binary 0 will term inate any C string!
This is because the \0 is defined as C string end tag. Therefore, the G SM 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 Table 4.
By the way, this may be the reason why even network providers often replace "@"with “@=*” in
their SIM application.
3. Other characters of the GSM alphabet are misinterpreted by an ASCII term inal program. For ex-
ample, GSM "ö" (as in "Börse") is assumed to be "|" in ASCII, thus result ing in "B|rse". This is be-
cause both alphabets mean different characters with values hex. 7C or 0 0 and so on.
4. In addition, decimal 17 and 19 which are used as XON/XOFF control char acters when software
flow control is activated, are interpreted as normal characters in th e GSM alphabet.
When you write characters differently coded in ASCII and GSM (e.g. Ä, Ö, Ü), you need to enter es-
cape sequences. Such a character is translated into the corres ponding GSM character value and,
when output later, the GSM character value can be presented. An y ASCII terminal then will show
wrong responses.
Table 4: Character definitions depending on alphabet (examples )
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
ò 08 BSP \08 5C 30 38
@ 00 NULL \00 5C 30 30
CAUTION: Often, the editors of terminal programs do not recognize escape se quences. In this case,
an escape sequence will be handled as normal characters. The most common workaround to this
problem is to write a script which includes a decimal code instead of an escape s equence. This way
you can write, for example, short messages which may contain differentl y coded characters.