MC68332
CENTRAL PROCESSING UNIT
USER’S MANUAL
5-13
5.8.2 Special Control Instructions
Low power stop (LPSTOP) and table lookup and interpolate (TBL) instructions have
been added to the MC68000 instruction set for use in controller applications.
5.8.2.1 Low Power Stop (LPSTOP)
In applications where power consumption is a consideration, the CPU32 forces the de-
vice into a low power standby mode when immediate processing is not required. The
low power stop mode is entered by executing the LPSTOP instruction. The processor
remains in this mode until a user-specified (or higher) interrupt level or reset occurs.
5.8.2.2 Table Lookup and Interpolate (TBL)
To maximize throughput for real-time applications, reference data is often precalculat-
ed and stored in memory for quick access. Storage of many data points can require
an inordinate amount of memory. The table instruction requires that only a sample of
data points be stored, reducing memory requirements. The TBL instruction recovers
intermediate values using linear interpolation. Results can be rounded with a round-
to-nearest algorithm.
5.9 Exception Processing
An exception is a special condition that preempts normal processing. Exception pro-
cessing is the transition from normal mode program execution to execution of a routine
that deals with an exception.
5.9.1 Exception Vectors
An exception vector is the address of a routine that handles an exception. The vector
base register (VBR) contains the base address of a 1024-byte exception vector table,
which consists of 256 exception vectors. Sixty-four vectors are defined by the proces-
sor, and 192 vectors are reserved for user definition as interrupt vectors. Except for
the reset vector, each vector in the table is one long word in length. The reset vector
is two long words in length. Refer to
for information on vector assignment.
CAUTION
Because there is no protection on the 64 processor-defined vectors,
external devices can access vectors reserved for internal purposes.
This practice is strongly discouraged.
All exception vectors, except the reset vector, are located in supervisor data space.
The reset vector is located in supervisor program space. Only the initial reset vector is
fixed in the processor memory map. When initialization is complete, there are no fixed
assignments. Since the VBR stores the vector table base address, the table can be
located anywhere in memory. It can also be dynamically relocated for each task exe-
cuted by an operating system.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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