UM10462
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User manual
Rev. 5.5 — 21 December 2016
425 of 523
NXP Semiconductors
UM10462
Chapter 21: LPC11U3x/2x/1x Serial Wire Debugger (SWD)
21.6 Functional description
21.6.1 Debug limitations
Important:
Due to limitations of the ARM Cortex-M0 integration, the LPC11U3x/2x/1x
cannot wake up in the usual manner from Deep-sleep mode. It is recommended not to
use this mode during debug.
Another issue is that debug mode changes the way in which reduced power modes work
internal to the ARM Cortex-M0 CPU, and this ripples through the entire system. These
differences mean that power measurements should not be made while debugging, the
results will be higher than during normal operation in an application.
During a debugging session, the System Tick Timer is automatically stopped whenever
the CPU is stopped. Other peripherals are not affected.
21.6.2 Debug connections for SWD
For debugging purposes, it is useful to provide access to the ISP entry pin PIO0_1. This
pin can be used to recover the part from configurations which would disable the SWD port
such as improper PLL configuration, reconfiguration of SWD pins as ADC inputs, entry
into Deep power-down mode out of reset, etc. This pin can be used for other functions
such as GPIO, but it should not be held LOW on power-up or reset.
Table 411. JTAG boundary scan pin description
Pin Name
Type
Description
TCK
Input
JTAG Test Clock.
This pin is the clock for JTAG boundary scan
when the RESET pin is LOW.
TMS
Input
JTAG Test Mode Select.
The TMS pin selects the next state in the
TAP state machine. This pin includes an internal pull-up and is used
for JTAG boundary scan when the RESET pin is LOW.
TDI
Input
JTAG Test Data In.
This is the serial data input for the shift register.
This pin includes an internal pull-up and is used for JTAG boundary
scan when the RESET pin is LOW.
TDO
Output
JTAG Test Data Output.
This is the serial data output from the shift
register. Data is shifted out of the device on the negative edge of the
TCK signal. This pin is used for JTAG boundary scan when the
RESET pin is LOW.
TRST
Input
JTAG Test Reset.
The TRST pin can be used to reset the test logic
within the debug logic. This pin includes an internal pull-up and is
used for JTAG boundary scan when the RESET pin is LOW.