I tried other serial communicator, and I'm not sure if I found the trouble...
Name: WithNewLine.png Views: 12996 Size: 46.5 KB
When I disable the Append New Line

Name: WithNewLine2.png Views: 13140 Size: 47.5 KB
With New line after sending

Do you think adding new line after each send will solve it - how?

Code:
HSEROUT ["AT",13] 
HSERIN 4000, GSM_CHECK_ERR, [WAIT("OK")]
The code above does not detect "OK".

regards,
tacbanon