User's Manual

Bluegiga Technologies Oy
Page 16 of 41
4.2 Other interfaces
4.2.1 Debug SPI interface
A separate SPI bus is provided at the module pads for device access during testing and uploading settings
during application development and manufacturing. This interface cannot be used as a host interface. It is
recommended to bring these to a connector or test pads in case RF certification measurements that cannot be
made through the host connection are required with the finished design. If it is not expected that certification
measurements would be needed, the debug SPI pads should be left unconnected. The pads do not need
external pull-ups when unconnected.
The debug SPI bus has logic levels set by the VDD_PADS reference supply line.
4.2.2 Bluetooth coexistence
Bluetooth coexistence systems allow co-located Wi-Fi and Bluetooth devices to be aware of each other and to
avoid simultaneous transfers that would degrade link performance. WF111 supports a number of different
coexistence schemes with up to 6 control lines for hardware communication between the two devices.
For reliable simultaneous communication both stacks need to be able to communicate together, in practice a
common driver system needs to be used so the packet priorities can be communicated between the stacks.
With separate stacks the only communication channel is the hardware interface and the devices have only
high and low priorities in use. As Wi-Fi data will automatically get higher priority than Bluetooth, high data
throughput on Wi-Fi may lead to poor Bluetooth operation when used simultaneously.
Wi-Fi and Bluetooth may use separate antennas, or share a single antenna through a switch. With a shared
antenna, usually two additional signals are needed to control the front end switch. WF111 contains an internal
switch for separating Wi-Fi and Bluetooth transmissions. (See chapter 7.3.)
For use with CSR-based Bluetooth (BC4 to BC6 with firmware version 21 or later, BC7 and onwards with all
versions), Unity-3e+ is recommended as the coexistence scheme. Unity-3e is an enhanced version of the 3-
wire Unity-3 –scheme that uses tighter timings and uses the three control lines also for antenna switch control,
removing the need for the two separate switch control lines. Unity-3e+, or Unity-3e with Unity+ adds an
additional BT_PERIODIC signal to communicate the need for a periodic transmission from the Bluetooth to
the Wi-Fi, allowing a guaranteed low-latency throughput for certain Bluetooth applications despite high Wi-Fi
usage. This allows reliable audio connections that would otherwise suffer from the Wi-Fi’s higher priority. Use
of Unity+ requires the use of a combined stack driver. Without software support, the periodic signaling cannot
be initialized.
Figure 7: Coexistence signals between WF111 and WT21 Bluetooth module (not showing antenna
sharing connection)