UM11029
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
491 of 515
NXP Semiconductors
UM11029
Chapter 31: LPC84x Serial Wire Debug (SWD)
31.5.3 Boundary scan
The RESET pin selects between the JTAG boundary scan (RESET = LOW) and the ARM
SWD debug (RESET = HIGH). The ARM SWD debug port is disabled while the part is in
reset.
To perform boundary scan testing, follow these steps:
1. Erase any user code residing in flash.
2. Power up the part with the RESET pin pulled HIGH externally.
3. Wait for at least 250
s.
4. Pull the RESET pin LOW externally.
5. Perform boundary scan operations.
6. Once the boundary scan operations are completed, assert the TRST pin to enable the
SWD debug mode and release the RESET pin (pull HIGH).
Remark:
The JTAG interface cannot be used for debug purposes.
Remark:
POR, BOD reset, or a LOW on the TRST pin puts the test TAP controller in the
Test-Logic Reset state. The first TCK clock while RESET = HIGH places the test TAP in
Run-Test Idle mode.
The VTREF pin on the SWD connector enables the debug connector to match the target voltage.
Fig 66. Connecting the SWD pins to a standard SWD connector
RESET
SWDIO
SWCLK
V
DD
LPC84x
ISP entry
PIO0_12
VTREF
SWDIO
SWCLK
nRESET
GND
from SWD
connector
3.3 V
~10 kΩ -
100 kΩ
DGND
~10 kΩ -
100 kΩ