User's Manual

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Laird Technologies

BTM410/411

Bluetooth

AT Data Module

INCOMING CONNECTIONS

The device can be conﬁ gured using the AT+BTP or AT+BTG command so that it will scan for incoming connec-

tions from other Bluetooth devices. It can also be conﬁ gured via S Register 512 to be in this mode by default on

power up.

When the lower layers detect an incoming call, a RING 123456789012 string is sent to the host every second.

The command ATA is used to accept the connection and ATH to reject it.

On connection, if the S0 Register is >=0 then conﬁ rmation to the host is in the form:-

CONNECT 123456789012

CONNECT 123456789012 A

CONNECT 123456789012 E

CONNECT 123456789012 AE

Where ‘A’ means authenticated connection and ‘E’ means encryption has been enabled.

When S0 register is -1, neither RING nor CONNECT is sent to the host and the connection is silently accepted.

If the S 100 register is non-zero, then after the ring indications speciﬁ ed by this register have been sent to

the host, and the host has failed to accept or reject the incoming connection, then an automatic ‘hangup’

is initiated.

DROPPING CONNECTIONS

In a conventional telephony modem, a call is normally terminated by ﬁ rst 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 Bluetooth modules provide a variety of ways of dropping a connection. One method is simi-

lar 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 200kbps. To cater for this performance hit,

the device’s connection drop capability is conﬁ gurable 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 ﬁ le 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 ﬁ le it is going to happen as fast as

possible and so the inter character gap is going to be signiﬁ cantly shorter than the <Guard time>.

The <Esc Chr> character can be changed via the S2 register and the <Guard time> interval can be speciﬁ ed

via the S12 register.

CONFIGURING

THE BTM410/411