S42/Central Software User Guide
1VV0301318 Rev. 3
– 2018-08-31
Reproduction forbidden without written authorization from Telit Communications S.p.A.- All Rights Reserved.
Page 59 of 66
10.
LE Connection Parameters
This chapter describes the kind of creating a BLE connection from the central device to the
peripheral device include the usage of the LE connection parameters.
10.1.
Create a Bluetooth Low Energy Connection
In a typical Bluetooth Low Energy system, the peripheral device advertises with specific data
letting any central device know that it is a connectable device. This advertisement contains the
device address, and can contain some additional data as well, such as the device name. The
central device, upon receiving the advertisement, sends a “scan request” to the peripheral. The
peripheral responds with a “scan response”. This is the process of device discovery, in that the
central device is now aware of the peripheral device, and knows that it can form a connection
with it. The central device can then send out a request to establish a link with the peripheral
device. A connection request contains a few connection parameters:
•
Connection Interval
In a BLE connection between two devices, a frequency-hopping scheme is used, in that the
two devices each send and receive data from one another on a specific channel, then “meet”
at a new channel (the link layer of the BLE stack handles the channel switching) at a specific
amount of time later. This “meeting” where the two devices send and receive data is known
as a “connection event”. Even if there is no application data to be sent or received, the two
devices will still exchange link layer data to maintain the connection. The connection
interval is the amount of time between two connection events, in units of 1.25ms. The
connection interval can range from a minimum value of 6 (7.5ms) to a maximum of 3200
(4.0s).
The S42/Central uses the configuration command AT+LECONINTMIN and
AT+LECONINTMAX to set these predefined values of the connection interval.
•
Slave Latency
This parameter gives the slave (peripheral) device the option of skipping a number of
connection events. This gives the peripheral device some flexibility, in that if it does not
have any data to send it can choose to skip connection events and stay asleep, thus providing
some power savings. The decision is up to the peripheral device.
The slave latency value represents the maximum number of events that can be skipped. It
can range from a minimum value of 0 (meaning that no connection events can be skipped)
to a maximum of 499; however the maximum value must not make the effective connection
interval (see below) greater than 32.0s.
The S42/Central uses the configuration command AT+LESLAVELAT to set the
predefined slave latency timeout value.
