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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
348 of 368
NXP Semiconductors
UM10375
Chapter 22: LPC13xx Serial Wire Debug (SWD)
22.6 Debug notes
22.6.1 Debug limitations
Important:
The user should be aware of certain limitations during debugging. The most
important is that, due to limitations of the ARM Cortex-M3 integration, the LPC13xx 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-M3 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.
Remark:
Note that the debug mode is not supported in any of the reduced power modes.
22.6.2 Debug connections
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 or 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 356. Serial Wire Debug pin description
Pin Name
Type
Description
SWCLK
Input
Serial Wire Clock.
This pin is the clock for debug logic when in the
Serial Wire Debug mode (SWDCLK).
SWDIO
Input /
Output
Serial wire debug data input/output.
The SWDIO pin is used by an
external debug tool to communicate with and control the LPC13xx.
SWO
Output
Serial Wire Output.
The SWO pin optionally provides data from the
ITM and/or the ETM for an external debug tool to evaluate.