MPC555 / MPC556
UNIFIED SYSTEM INTERFACE UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
5-1
SECTION 5
UNIFIED SYSTEM INTERFACE UNIT
The unified system interface unit (USIU) of the MPC555 / MPC556 controls system
start-up, system initialization and operation, system protection, and the external sys-
tem bus. The MPC555 / MPC556 USIU functions include the following:
• System configuration and protection
• Interrupt controller
• System reset monitoring and generation
• Clock synthesizer
• Power management
• External bus interface (EBI) control
• Memory controller
• Debug support
5.1 Module Overview
The system configuration and protection function controls the overall system configu-
ration and provides various monitors and timers, including the bus monitor, software
watchdog timer, periodic interrupt timer, PowerPC decrementer, time base, and real
time clock. The interrupt controller and USIU are also included in the system configu-
ration and protection function. Refer to
SECTION 6 SYSTEM CONFIGURATION AND
for details.
The reset controller receives input from a number of reset sources and takes appro-
priate actions, depending on the source. The reset status register (RSR) reflects the
most recent source to cause a reset. Refer to
for details.
The clock synthesizer generates the clock signals used by the SIU as well as the other
modules and external devices. This circuitry can generate the system clock from a 4-
MHz or 20-MHz crystal.
The SIU supports various low-power modes. Each supplies a different range of power
consumption, functionality and wake-up time. Clock generation and low-power modes
are described in
SECTION 8 CLOCKS AND POWER CONTROL
The external bus interface (EBI) handles the transfer of information between the inter-
nal busses and the memory or peripherals in the external address space. The
MPC555 / MPC556 is designed to allow external bus masters to request and obtain
mastership of the system bus, and if required access the on-chip memory and regis-
ters.
SECTION 9 EXTERNAL BUS INTERFACE
describes the bus operation.
The memory controller module provides a glueless interface to many types of memory
devices and peripherals. It supports up to four memory banks, each with its own device
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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