Laird BTM410, User Manual, Page: 29 / 78

BTM410/411
Bluetooth
®
AT Data Module
29 www.lairdtech.com Laird Technologies
AT COMMAND SET
REFERENCE
5. ATO {Enter Data Mode} (letter ‘o’)
Return to data mode. Assume that the module is in data mode after OK is received. Responds with
an error if there is no Bluetooth SSO connection.
Response:
<cr,lf> CONNECT 123456789012, << cr,lf> (if it was an incoming connection)
<cr,lf> CONNECT 123456789012, >< cr,lf> (if it was an outgoing connection)
Or
Response: <cr,lf>ERROR nn<cr,lf>
6. Dropping SSO Connections
In a conventional telephony modem, a call is normally terminated by first sending a +++ character
sequence enveloped by an escape sequence guard time (of the order of 100 to 1000 milliseconds)
to enter local command and connected mode and then the ATH command.
Laird Technologies BTM devices provide a variety of ways of dropping a connection. One method is
similar to the above, but instead a ^^^ character sequence is used. This is to eliminate ambiguity
when a data call is in progress via a mobile phone which was established using the mobile phone’s
Bluetooth AT modem. The second method involves the host dropping the DTR (DSR from the
module’s viewpoint) handshaking line.
Being able to drop a connection using the escape sequence ^^^ has a severe penalty on data
throughput. In fact, the data rate is of the order of 85kbps instead of about 300kbps. To cater for
this performance hit, the device’s connection drop capability is configurable to be in one of two
modes. One mode allows for a connection to be dropped using either method, and the other mode
allows for a connection drop using the DTR method only. By default, the device is in the former
mode. This mode is selected using the S507 register (
Appendix , Table 4-1).
To reiterate, the escape sequence is as follows:-
<Guard time><Esc Chr><Guard time><Esc Chr><Guard time><Esc Chr><Guard time>
This means that even when a file transfer is occurring and it happens to be full of <Esc Chr>
characters then it is not going to drop into command mode because, when transferring a file it is
going to happen as fast as possible and so the inter character gap is going to be significantly
shorter than the <Guard time>.
The <Esc Chr> character can be changed via the S2 register and the <Guard time> interval can be
specified via the S12 register (
Appendix , Table 4-1).
7. SSO - Asynchronous Messages
RX<string>
This response is sent to the host when the unit is in online-command mode and S Register 531 is set
to 3 and data arrives from a peer.
If the data from the string contains non-visual characters (for example ASCII 0 to 31 and ASCII 128
to 255), then those characters are translated into a 3 character escape sequence starting with ‘\’.
For example the embedded <cr><lf> sequence would be sent as the 6 character string \0D\0A.
If the data contains the character ‘“’ then it is sent as \22.
If the data contains the character ‘\’ then it is sent as \5C