Motorola MPC823e User Manual

Reset
4-2 MPC823e REFERENCE MANUAL MOTOROLA
RESET
4
4.1 TYPES OF RESET
The MPC823e has several types of inputs to the reset logic:
• Power-on reset
• External hard reset
• Internal hard reset
❏ Loss of lock
❏ Software watchdog reset
❏ Checkstop reset
❏ Debug port hard reset
❏ JTAG reset
• External soft reset
• Internal soft reset
❏ Debug port soft reset
❏ JTAG soft reset
All of these reset sources are fed into the reset controller and, depending on the source of
the reset, different actions are taken. The reset status register reflects the last source to
cause a reset.
4.1.1 Power-On Reset
PORESET
(power-on reset) is an active low input pin. In a system with power-down
low-power mode, this pin must only be activated when a voltage in the keep-alive power
(KAPWR) rail fails. When this pin is asserted, the MODCK bits are sampled and the
phase-locked loop multiplication factor and pitrtclk and tmbclk sources are changed to their
default values. When this pin is negated, internal MODCK values are unchanged. The
PORESET
pin must be asserted for a minimum of 3 microseconds. After detecting this
assertion, the MPC823e enters the power-on reset state and stays there until the following
events occur:
• The internal PLL enters the lock state and the system clock is active
• The PORESET
pin is negated
When PORESET
is asserted, the MPC823e enters the power-on reset (POR) state in which
SRESET
and HRESET are asserted by the core. When the MPC823e remains in POR, the
extension counter of 512 is reset, and the MODCK pins are sampled when POR pin is
negated. After the negation of PORESET
and the PLL locks, the core enters the state of
internal initiated HRESET
and continues driving the HRESET and SRESET pins for 512
cycles. When the timer expires, which is usually after the 512 cycles, the configuration is
sampled from the data pins and the core stops driving the pins. An external pull-up resistor
should drive the HRESET
and SRESET pins high. After the pins are negated, a 16-cycle
period passes before the presence of an external (hard/soft) reset is tested. Refer to
Section 4.3.1 Hard Reset for more information.

Motorola MPC823e Specifications

General

Brand	Motorola
Model	MPC823e
Category	Computer Hardware
Language	English