The following signals are necessary for RX direct mode

RX data clock output

RX data output

You can assign them to any radio GPIO pin by setting the corresponding GPIO_MODE to RX_DATA_CLK or RX_DATA via the GPIO_PIN_CFG command.

The following signals are necessary for TX direct mode

TX data clock output

You can assign it to any radio GPIO pin by setting the corresponding GPIO_MODE to TX_DATA_CLK via the GPIO_PIN_CFG command.

TX data input

The TX_DIRECT_MODE_GPIO field of the MODEM_MOD_TYPE property determines which radio GPIO pin is selected as the modulation data source during TX Direct mode. Also the GPIO_MODE of the corresponding radio GPIO has to be set to INPUT via the GPIO_PIN_CFG command.

When generating the configuration from WDS, GPIO mode can be selected on the "GPIO and FRR" tab of the configurator. However the TX_DIRECT_MODE_GPIO field is left by WDS always in the default GPIO0 setting and can be modified only by hand in the generated config header.

Note 1: For Si4x55 the TX data input can be assigned only to GPIO0.

Note 2: For active signals like data and clock, the GPIO0 and GPIO1 pins should be primarily used , because these have less susceptibility to generating spurious components in the synthesizer than GPIO2 and GPIO3 have.