Multi-Tech MultiModem EDGE Reference Manual page 14

1.5.2.2 Implementing Input of Terminal Data to SIM (Direction TE to TA)
Used Character
Set
GSM
UCS2
The ratio between the number of input characters and bytes stored on the SIM is given in
Note:
parentheses.
Case 1
Every character is sent from TE to TA as GSM character (or ASCII with HyperTerminal).
Character value must be in range from 0 to 127 because of 7-bit GSM alphabet.
To reach maximum SMS text length of 160 characters in 140 bytes space characters will be compressed on SIM.
This must be set using the parameter <dcs> of AT+CSMP (add 64).
Example: "ABCDEFGH" typed is sent and stored uncompressed as
compressed as 41E19058341E91'H).
Case 2
Every data byte is sent to TA as 2 IRA characters.
Maximum text length is 280 IRA characters which will be converted into 140 bytes SMS binary user data.
Example: "C8" typed is sent as 43'H, 38'H
Case 3
Every 16-bit value is sent to TA as 4 IRA characters.
Maximum text length is 280 IRA characters which will be converted into 70 UCS2 characters (16-bit each).
Number of IRA characters must be a multiple of four because always 4 half bytes are needed for a 16-bit value.
Example: "D2C8" typed is sent as 44'H, 32'H, 43'H, 38'H
Case 4
Every GSM character is sent to TA as 4 IRA characters representing one UCS2 character.
Example: To store text "ABC" using UCS2 character set you have to type "004100420043".
This is sent as 30'H,30'H,34'H,31'H, 30'H,30'H,34'H,32'H, 30'H,30'H,34'H,33'H
representation of 3 UCS2 characters, converted to GSM character set and stored as 41'H, 42'H, 43'H.
Maximum input is 640 IRA characters representing 160 UCS2 characters when compression is active. These are
converted to 160 GSM 7-bit characters.
Without compression only 140 GSM characters can be stored which are put in as 560 IRA characters.
Values of UCS2 characters must be smaller than 80'H (128 decimal) to be valid GSM characters.
Number of IRA characters must be a multiple of four. Problems:
•
"41" ¨ Error, there are four IRA characters (two bytes) needed
• "0000" Error, not an UCS2 character
•
"4142" Error, value of UCS2 character > 7F'H
• "008B" Error, value of UCS2 character > 7F'H
This affects the maximum input length of a string)
Case 5
Every UCS2 character is sent as 4 IRA characters and is converted into two 8-bit values. This means that the
first two characters have to be '00'.
Example: UCS2 character 009F'H typed as "009F" is sent as 30'H,30'H,39'H,46'H ¨ converted into 8-bit value
9F'H.
Maximum number of UCS2 characters is 140 which are represented by 560 IRA characters. Number of IRA
characters must be a multiple of four.
Case 6
Every UCS2 character is sent as 4 IRA characters each and is converted into a 16-bit value again.
Example: UCS2 character 9F3A'H typed as "9F3A" is sent as 39'H,46'H,33'H,41'H
Maximum number of UCS2 characters is 70 which are represented by 280 IRA characters. Number of IRA
characters must be a multiple of four.
Invalid UCS2 values must be prevented.
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371G)
DCS = 7 bit DCS = 8 bit
GSM Data
Case 1 Case 2
GSM (1:1) IRA to 8 bit (2:1)
Case 4 Case 5
GSM to IRA (1:4) 8 bit to IRA (1:4)
stored as C8'H.
DCS = 16 bit
UCS2
Case 3
IRA to 16 bit (4:2)
Case 6
UCS2 to IRA (2:4)
4142434445464748'H (stored
stored as D2C8'H.
detected as IRA
converted into 9F3A'H.
Chapter 1 – Introduction
14