
Reset
4-2
MPC823 USER’S MANUAL
MOTOROLA
RESET
4
4.1 TYPES OF RESET
The MPC823 has several types of inputs to the reset logic:
Power-on reset
External hard reset
Internal hard reset
t Loss of lock
t Software watchdog reset
t Checkstop reset
t Debug port hard reset
t JTAG reset
External soft reset
Internal soft reset
t Debug port soft reset
t 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 should 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 should be asserted for a minimum of 3 microseconds. After detecting this
assertion, the MPC823 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 MPC823 enters the power-on reset (POR) state in which
SRESET and HRESET are asserted by the core. When the MPC823 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 or PLL lock, 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