M66 & SMS, how to use GSM default alphabet character set, 7-bit coded

I’m using M66 for SMS alarming. All works fine till SMS text contains ‘_’ character (underscore). Received SMS on phone shows ‘§’ instead of ‘_’ character.

I tried to find why: Standard ASCII code for ‘_’ character on computer is 0x5F.

M66 is set to GSM default alphabet, 7-bit coded by GSM 03.38. Checked by AT+CSCS=?, it reports answer +CSCS: “GSM”. I expect that it corresponds with folowing character table:

There I found the answer, because standard ASCII code 0x5F corresponds in 7bit basic character set to ‘§’ character. Character ‘_’ corresponds with code 0x11. But when I send code 0x11 in SMS text, then I see ‘@’ on mobile phone. Why?

Later I tried to send characters from 0x00 to 0x19 as part of SMS text, but they are shown on phone as ‘@’ character too (except of CR, LF and CTRL+Z of course).

How to show characters in range from 0x00 to 0x1F from 7bit basic character set on mobile phone SMS? Or at least, how to show ‘_’ character, please?

Dear Sir,
For your issue, you can try to set AT+CSCS=“IRA” to have a try. Thanks!

or You can try AT+CSCS=“8859-1”