The LTE modem uses a dedicated three-pin interface for RF interference avoidance towards a companion radio device such as an external positioning device or Bluetooth® Low Energy device.
The inputs and outputs for this interface are the following:
- COEX0 – Input to the LTE modem from the external device. When active high, indicates that the external device transceiver is turned on. When internal GPS is used, COEX0 can be used as active high control for the external LNA component.
- COEX1 – Output from the LTE modem to the external device. Active high time mark pulse, which is synchronous to LTE system time. When internal GPS is used, COEX1 delivers the GPS 1PPS (one pulse per second) time mark pulse.
- COEX2 – Output from the LTE modem to the external device. When active high, indicates that the LTE modem transceiver is turned on. COEX2 can also be treated as active low grant from LTE modem to the external device, indicating grant to transmit and receive.
Note: Using the COEX2 pin requires an external pull-down resistor in the 100 kΩ size range.
Note: For information on COEX signaling feature support, see the nRF9160 Modem Firmware Release Notes included in the latest nRF9160 modem firmware.
The COEX interface timing in relation to modem state is shown in the following figure.
Figure 1. COEX interface timing
