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MOTOROLA
MPC801 USER’S MANUAL
12-1
12
SECTION 12
SYSTEM INTERFACE UNIT
This section summarizes the MPC801 system interface unit (SIU) functions that control
system startup, initialization, operation, protection, and the external bus. The system
configuration and protection function controls the overall system and provides various
monitors and timers, including the bus monitor, software watchdog timer, periodic interrupt
timer, PowerPC
decrementer, timebase, and real-time clock. The clock synthesizer
generates the clock signals and other modules and external devices that the system
interface unit uses. This circuitry generates the system clock from an inexpensive
32KHz/4MHz crystal. The system interface unit supports various low-power modes and
each one supplies a different range of power consumption, functionality, and wake-up time.
The clock scheme supports low-power modes for applications that use the baud rate
generators and/or serial ports during standby mode. The main system clock can be changed
dynamically while the baud rate generators and serial ports work with a fixed frequency. For
more information, refer to
Section 5 Clocks and Power Control
.
The external bus interface (EBI) handles the transfer of information between the internal
buses and the memory or peripherals in the external address space. The MPC801 is
designed to allow external bus masters to request and obtain mastership of the system bus.
Section 13 External Bus Interface
describes the bus operation, but the configuration
control of the external bus interface is explained in this section. The memory controller
module provides a glueless interface to many types of memory devices and peripherals. It
supports a maximum of eight memory banks, each with its own device and timing attributes.
Memory control services are provided to both internal and external masters.
NOTE
The chip’s address bus is 26 bits wide, but the internal address
bus is 32 bits wide. Therefore, external accesses are internally
considered 26 bit accesses (A[6–31]) with A[0–5] equal to 0,
while internal accesses are full 32-bit accesses.
The MPC801 implementation supports circuit board test strategies through a
user-accessible test logic that is fully compliant with
Port
.
Section 19 IEEE 1149.1 Test Access