UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
129 of 515
NXP Semiconductors
UM11029
Chapter 10: LPC84x Switch matrix (SWM)
10.4 General description
The switch matrix connects internal signals (functions) to external pins. Functions are
signals coming from or going to a single pin on the package and coming from or going to
an on-chip peripheral block. Examples of functions are the GPIOs, the UART transmit
output (TXD), or the clock output CLKOUT. Many peripherals have several functions that
must be connected to external pins.
The switch matrix also enables the output driver for digital functions that are outputs. The
electrical pin characteristics for both inputs and outputs (internal pull-up/down resistors,
inverter, digital filter, open-drain mode) are configured by the IOCON block for each pin.
Most functions can be assigned through the switch matrix to any external pin that is not a
power or ground pin. These functions are called movable functions.
A few functions like the crystal oscillator pins (XTALIN/XTALOUT) or the analog
comparator inputs can only be assigned to one particular external pin with the appropriate
electrical characteristics. These functions are called fixed-pin functions. If a fixed-pin
function is not used, it can be replaced by any other movable function.
For fixed-pin analog functions, the switch matrix enables the analog input or output and
disables the digital pad.
GPIOs are special fixed-pin functions. Each GPIO is assigned to one and only one
external pin by default. External pins are therefore identified by their fixed-pin GPIO
function. The level on a digital input is always reflected in the GPIO port register and in the
pin interrupt/pattern match state, if selected, regardless of which (digital) function is
assigned to the pin through the switch matrix.
Fig 13. Functional diagram of the switch matrix
GPIO
PIO0_m
SYSCON
PINTSEL[7:0]
PIN
INTERRUPT
SWM
IOCON
USART0
ANALOG
PERIPHERAL
DIGITAL
PERIPHERAL
DIGITAL
PERIPHERAL
PIO0_m
DIGITAL PAD
ANALOG PAD
digital input
digital output
digital output ena
analog ena
analog i/o
package
pin x
U0_RXD
U0_CTS
U0_SCLK
U0_TXD
U0_RTS
GPIO_INT_BMAT