UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
127 of 515
NXP Semiconductors
UM11029
Chapter 10: LPC84x Switch matrix (SWM)
10.3.1 Connect an internal signal to a package pin
The switch matrix connects all internal signals listed in the table of movable functions
through the pin assignment registers to external pins on the package. External pins are
identified by their default GPIO pin number PIO0_n or PIO1_(n-32). Follow these steps to
connect an internal signal FUNC to an external pin. An example of a movable function is
the UART transmit signal TXD:
1. Find the pin function in the list of movable functions in
2. Use the LPC84x data sheet to decide which pin x on the LPC84x package to connect
the pin function to.
3. Use the pin description table to find the default GPIO function PIO0_n or PIO1_(n-32)
assigned to package pin x. m is the pin number.
4. Locate the pin assignment register for the function FUNC in the switch matrix register
description.
5. Disable any special functions on pin PIO0_n in the PINENABLE0 register or
PIO1_(n-32) in the PINENABLE1 register.
6. Program the pin number n into the bits assigned to the pin function.
The pin function is now connected to pin x on the package.
A pin is identified for the purpose of programming the switch matrix by its default GPIO port pin number.
Fig 12. Example: Connect function U0_RXD and U0_TXD to pins 4 and 14
PIO0_8 ->
pin number 8
disable XTALIN
PINENABLE0 bit 4 = 1
assign U0_TXD
PINASSIGN0 bits 7:0 = 0x8
function U0_TXD
assigned to pin 14
PIO0_12 ->
pin number 12
assign U0_RXD
PINASSIGN0 bits 15:8 = 0x10
function U0_RXD
assigned to pin 4
PIO0_8/XTALIN
PIO0_12
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