There are different types of connections available for the BLE device. A BLE connected item may have up to 4 different functions:
The "Broadcaster" shall be used as a server. Thus, its purpose is to transfer data to a device on a regular basis, but it does not support any incoming connection.
A typical example is Beacon based on Bluetooth Low Energy.When the beacon is in the broadcast mode, it is generally set to a non-connectable state. Beacon will broadcast a data packet to the surroundings at regular intervals. As an independent Bluetooth host, it will receive Beacon broadcasts at intervals when performing scanning actions Out of the packet. The content of the packet can contain up to 31 bytes of content. At the same time, when the host receives the broadcast packet, it will indicate the MAC address, Received Signal Strength Indicator (RSSI), and some application-related advertising data.The picture below is Feasycom BP103:
In a second step, the device may only monitor and read the data sent by a "broadcaster". In such a case, the object is not able to send any connection to the server.
A typical example is Gateway. BLE Bluetooth is in observer mode, no broadcast, it can scan the surrounding broadcast equipment, but can not require connection with the broadcast equipment. The picture below is Feasycom Gateway BP201:
Central usually consists of a smartphone or tablet. This device provides two different types of connection: either in advertising mode or in connected mode. It is leading the overall process as it triggers data transfer. The picture below is Feasycom BT630, based on nRF52832 chipset, it supports three modes: central, peripheral, central-peripheral.
Peripheral device allows connections and data transfer with the Central on a periodical basis. This system´s goal is to ensure universal data transmission by using the standard process, so that other devices also may read and understand the data.
The Bluetooth Low Energy module working in peripheral mode is also in the broadcast state, waiting to be scanned. Unlike the broadcast mode, the Bluetooth module in the slave mode can be connected, and acts as a slave during data transmission.
Most of our BLE modules could support central plus peripheral mode. But we have firmware supporting peripheral-only mode, the picture below is Feasycom BT616, it has firmware supporting peripheral-only mode: