Product Info

Bluetooth Serial Module

AT Command Set

Date : 3 Feb 03 Issue No : 1.9 Doc No : XRBLU020-001SW-0 Page 21 of 38

5. Dropping 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) and

then the ATH command.

This device will provide a couple of ways of dropping a connection. One method will be 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 will involve 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 200kbps. 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 former mode. This mode is

selected using the S507 register. See S register table described in an earlier section.

To reiterate, the escape sequence is as follows:-

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.