Philips LPC2101 User Manual page 34

Philips Semiconductors
Volume 1
timer"
de-asserted, the oscillator is running, a fixed number of clocks have passed, and the
on-chip circuitry has completed its initialization. The relationship between Reset, the
oscillator, and the wake-up timer are shown in
The Reset glitch filter allows the processor to ignore external reset pulses that are very
short, and also determines the minimum duration of RESET that must be asserted in
order to guarantee a chip reset. Once asserted, RESET pin can be deasserted only when
crystal oscillator is fully running and an adequate signal is present on the X1 pin of the
microcontroller. Assuming that an external crystal is used in the crystal oscillator
subsystem, after power on, the RESET pin should be asserted for 10 ms. For all
subsequent resets when crystal oscillator is already running and stable signal is on the X1
pin, the RESET pin needs to be asserted for 300 ns only.
When the internal Reset is removed, the processor begins executing at address 0, which
is initially the Reset vector mapped from the Boot Block. At that point, all of the processor
and peripheral registers have been initialized to predetermined values.
External and internal Resets have some small differences. An external Reset causes the
value of certain pins to be latched to configure the part. External circuitry cannot
determine when an internal Reset occurs in order to allow setting up those special pins,
so those latches are not reloaded during an internal Reset. Pin 26 (RTCK) is examined
during an external Reset (see
P0.14 (see
code is executed after every Reset.
It is possible for a chip Reset to occur during a Flash programming or erase operation.
The Flash memory will interrupt the ongoing operation and hold off the completion of
Reset to the CPU until internal Flash high voltages have settled.
User manual
in this chapter), causing reset to remain asserted until the external Reset is
Section 19.4 on page
Rev. 01 — 12 January 2006
Figure 10.
Section 6.2 on page 61
229) is examined by the on-chip bootloader when this
UM10161
Chapter 3: System control block
and Section 7.4 on page
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
66). Pin
34