LPC2925 NXP Semiconductors, LPC2925 Datasheet - Page 12

• Manufacturer Part Number: LPC2925
• Description: (LPC2921 - LPC2925) ARM9 microcontroller
• Manufacturer: NXP Semiconductors

NXP Semiconductors
1.
LPC2921_2923_2925_0
Preliminary data sheet
www.DataSheet4U.com
Only for 1.8 V power sources
6.6.1 Reset and power-up behavior
6.6.2 Reset strategy
6.6.3 IEEE 1149.1 interface pins (JTAG boundary-scan test)
6.6 Reset, debug, test, and power description
The LPC2921/2923/2925 contains external reset input and internal power-up reset
circuits. This ensures that a reset is extended internally until the oscillators and flash have
reached a stable state. See
See
shows the reset pin.
Table 4.
At activation of the RST_N pin the JTAGSEL pin is sensed as logic LOW. If this is the case
the LPC2921/2923/2925 is assumed to be connected to debug hardware, and internal
circuits re-program the source for the BASE_SYS_CLK to be the crystal oscillator instead
of the Low-Power Ring Oscillator (LP_OSC). This is required because the clock rate when
running at LP_OSC speed is too low for the external debugging environment.
The LPC2921/2923/2925 contains a central module, the Reset Generator Unit (RGU) in
the Power, Clock and Reset Subsystem (PCRSS), which controls all internal reset signals
towards the peripheral modules. The RGU provides individual reset control as well as the
monitoring functions needed for tracing a reset back to source.
The LPC2921/2923/2925 contains boundary-scan test logic according to IEEE 1149.1,
also referred to in this document as Joint Test Action Group (JTAG). The boundary-scan
test pins can be used to connect a debugger probe for the embedded ARM processor. Pin
JTAGSEL selects between boundary-scan mode and debug mode.
boundary- scan test pins.
Table 5.
Symbol
RST_N
Symbol
JTAGSEL
TRST_N
TMS
TDI
TDO
TCK
Section 9
Reset pin
IEEE 1149.1 boundary-scan test and debug interface
Direction
IN
for characteristics of the several start-up and initialization times.
Description
TAP controller select input. LOW level selects ARM debug mode and HIGH level
selects boundary scan and flash programming; pulled up internally
test reset input; pulled up internally (active LOW)
test mode select input; pulled up internally
test data input, pulled up internally
test data output
test clock input
Rev. 00.01 — 24 October 2008
Description
external reset input, active LOW; pulled up internally
Section 8
for trip levels of the internal power-up reset circuit
ARM9 microcontroller with CAN and LIN
LPC2921/2923/2925
Table 5
© NXP B.V. 2008. All rights reserved.
shows the
Table 4
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