Pin Control and Pin Function Selection (LPC40xx)


Learn about the selectable features of pins in the LPC40xx MCU, how to enable/disable these features and how to, select a pin's functionality.

Pin Features

The LPC40xx series chips have pins with the following features

see chapter Chapter 6: LPC408x/407x Pin configuration & Chapter 7: LPC408x/407x I/O configuration

Figure 1. I/O configurations Signals Highlighted (UM10562 LPC40xx Page 122)

  • Open Drain Enable: Enabling this disables the high side MOSFET in of the totem pole configuration, making that pin an open drain.
  • Pin Modes (Only one or none of these can be active at once)
    • Pull-Up Enable:Enabling this turns on the weak pull-down MOSFET in the ohmic region.
    • Pull-Down Enable: Enabling this turns on the weak pull-down MOSFET in the ohmic region.
    • Repeater Mode Enable: Enabling this, will activate the pull up or pull down resistor from the last.
  • Enable Input Invert: Converts a pin configured as an input to active low.
  • Enable Glitch Filter: Enables the 10nS glitch filter.
  • Enable Analog Input: Disables schmitt trigger and enables voltage to pass through analog switch to analog input.
  • There are actually more controls then this depending on the pin type you are using.


Figure 2. Type D IOCON registers (page 132)