The BIU threshold is a configurable value in the Threshold Noise register [Offset 0x30]. The default value of this register is 87 dBuV [0x03]. If noise or a signal is present on the powerline with a frequency near the carrier frequency of ~132kHz and an amplitude greater than 87 dBuV at the FSK_IN pin, the BIU will trigger and prevent transmission. The BIU threshold can be configured as each powerline has different line characteristics.
The available values can be found in the CY8CPLC10 data sheet or the PLT User Module datasheet in PSoC Designer. If you are using PSoC Designer, the value can be configured using the PLT User Module property Noise Level Threshold. Note that this property is only available for the “FSK Modem” and “FSK Modem + Network Stack” selection. The “FSK Modem + Network Stack + I2C Bridge” selection and the CY8CPLC10 device require an external host to change this value by writing to the Threshold Noise register.
The BIU can also be disabled completely by setting the Disable BIU bit in the PLC Mode register [Offset 0x05].