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 10 of 66
3.
Modes and Connections
In AT command mode the S42/Central supports 3 parallel central connections or one
peripheral Terminal I/O server connection. This means that the S42/Central stops
advertising (being connectable) as peripheral as soon a central connection is established.
When a peripheral Terminal I/O server connection is active, it is not possible to establish a
central connection to be used as GATT client.
The reason for this behavior is that a Terminal I/O connection in AT mode puts the serial
interface in data mode, where it is not possible to handle AT commands or events for an
additional central connection. Therefore it is not possible to use the ATD command for
connection establishment during a Terminal I/O connection.
To use peripheral and central connections in parallel the S42/Central supports the
multiplexing (MUX) mode. In this mode there is an always accessible AT command channel.
This makes it possible to handle all 4 links in parallel (3 central connections and one peripheral
Terminal I/O server connection). The host has to implement the simple to use multiplexing
protocol.
3.1.
AT Command Mode
This chapter describes connection examples for different roles:
•
Central role: GATT client connections to BLE peripheral devices in AT command mode
•
Peripheral role as Terminal I/O server
3.1.1.
Central Role as GATT Client
In central role the S42/Central supports the possibility to connect to any Bluetooth
low energy peripheral devices.
The following example lists the GATT connection in multiple steps include an explanation of
the different result messages.
