Table of Contents
Advertisement
SECTION
V.
THEORY OF OPERATION
5.1
MC68B09E/MBL68B09E/HD68BO9E
(IC1)
The heart
of any
computer system
is
the
Central Processing Unit) CPU.
In
the
Color Computer
3,
as
well
as in
most modern microprocessors,
the
CPU
is
a
single Large Scale Integration
Circuit (LSI). The CPU gathers
instructions and data from memory,
interprets and executes
the
instructions, and stores
the
results
of the
data operations
into memory.
Additionally,
the CPU stores
data
to
and retrieves data from various
input/output
(I/O) devices.
The 68B09E
microprocessor
is
perhaps
the
most powerful 8-bit
microprocessor available
today.
There
are several ways
to
determine
the
"size"
of
a
microprocessor (whether
it
is
8-bit, 16-bit, 32-bit, or
whatever)
.
One way involves
the
number
of
data interconnecting
lines
the
processor possesses. Another
is
the size of the
internal registers
and
the size of the
mathematical
and
logical operations supported by
the
processor. Although
the
68B09E has
an
8-bit data bus, internally
it
contains
four
16-bit registers and
two
additional 8-bit registers which
may
be linked together to form
another 16-bit register. The 68B09E
also supports
some 16-bit
mathematical
and logical operations.
Therefore, although
it
is
technically
an 8-bit processor,
it
has some of
the
power
of the 16-bit
machines.
Figure
5-1
is
a
"programming model"
of the 68B09E CPU.
Additional
information may
be
obtained from
the
68B09E data
sheet.
X —
Index
Register
Y
—
Index
Register
U
-
User Stack
Pointer
S
—
Hardware
Stack Pointer
PC
—
v-
D
E
Pointer Registers
Program Counter
Accumulators
Direct
Page
Register
CC
—
Condition
Code
Register
Carry
Overflow
Zero
Negative
IRQ
Mask
Half
Carry
FIRQMask
Entire Flag
Figure
5-1.
68B09E Programming Model
-30-
Advertisement
Chapters
Table of Contents
