Physical Configuration

The RSL15 system includes physical configuration parameters for each GPIO. These parameters are set using configuration bits from the appropriate GPIO_CFG_* registers.

If the GPIO is configured as an input pad, the GPIO_CFG_PULL_CTRL bit field is used to configure the pad to use a pull-up or pull-down resistor. Options include:

• No pull resistor
• A weak (250 kΩ) pull-up resistor
• A weak (250 kΩ) pull-down resistor
• A strong (10 kΩ) pull-up resistor

In the reset state — for example, when the NRESET pad is driven low — the GPIO output drive is disabled and a weak (250 kΩ) pull-up resistor is enabled. After reset is released, the default GPIO configuration is applied.

The GPIO_CFG_LPF bits in the GPIO_CFG registers enables or disables a low-pass filter that can be used to clean up the GPIO’s received input signal.

IMPORTANT: For optimal noise performance, we recommend enabling the low-pass filters provided for GPIO inputs when using input signals received at 1 MHz or less. For signals that use a frequency exceeding 1 MHz, the GPIO low-pass filters need to be disabled.

NOTE: When switching from disabled to GPIO output mode:

• From an input mode, the initial output value matches the value that has most recently been read from the input.
• From another output mode, the initial output value matches the current output value.
• The initial output value matches the value shown in the GPIO_OUTPUT_DATA register.

IMPORTANT: When a GPIO is configured as output, its value is based on its previous GPIO data register. Therefore, before configuring a GPIO to produce a specific output level, the application must set the GPIO register first and then configure the GPIO as an output.

If the GPIO is configured as an output pad, the GPIO_CFG_DRIVE bit allows you to select the drive strength for the GPIO output, with settings for 2x, 3x, 5x, and 6x the normal drive strength.