примерно так
LOCAL hPort, lnErr
lcPort="COM1"
hPort = CreateFile(lcPort, GENERIC_READ+GENERIC_WRITE , 0,0,;
OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0)
?hPort
IF hPort = INVALID_HANDLE_VALUE
lnErr = GetLastError()
RETURN "Error " + LTRIM(STR(lnErr)) + ". " + GetErrorMessage(lnErr)
ELSE
myStr='AT'+CHR(13)
aa=0
ss=WriteFile(hPort,@myStr,5,1,0)
?aa,ss
= CloseHandle(hPort)
RETURN "Ok"
ENDIF