UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
490 of 515
NXP Semiconductors
UM11029
Chapter 31: LPC84x Serial Wire Debug (SWD)
The boundary scan mode and the pins needed are selected by hardware (see
). There is no access to the boundary scan pins through the switch matrix.
Remark:
If SWD is disabled in the FAIM configuration, these pins will be configured as
GPIO pins on POR.
31.5 Functional description
31.5.1 Debug limitations
It is recommended not to use the debug mode during Deep-sleep or Power-down mode.
During a debugging session, the System Tick Timer is automatically stopped whenever
the CPU is stopped. Other peripherals are not affected.
31.5.2 Debug connections for SWD
For debugging purposes, it is useful to provide access to the ISP entry pin PIO0_12. This
pin can be used to recover the part from configurations which would disable the SWD port
such as improper PLL configuration, re-configuration of SWD pins, 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 477. JTAG boundary scan pin description
Function Pin name
Type
Description
TCK
SWCLK/PIO0_3/
TCK
I
JTAG Test Clock.
This pin is the clock for JTAG boundary scan when the RESET
pin is LOW.
TMS
SWDIO/PIO0_2/
TMS
I
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
PIO0_1/ACMP_I2/
CLKIN/TDI
I
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
PIO0_0/ACMP_I1/
TDO
O
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
PIO0_4/
WAKEUP/TRST/
ADC_11
I
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.