MC6800 Datasheet, PDF (12/32 Pages) Motorola, Inc – 8-BIT MICROPROCESSING UNIT (MPU)

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FIGURE13 – HALT AND SINGLE INSTRUCTION =ECUTION FOR SYSTEM DEBUG
@l
@z
m
BA
VMA
R/%
Address
Bus
Data
Bus
Instruction
m
x XY
\
x XY
Fetch
Addr M
x^Exwute
Instruction
Fetch
Instruction
Execute
{1
/
))
,
.,
:.~~>),
The M PU has three 16-bit registers and thra-$,8~*@
registers available for use by the programmer (FJ$’@?~d@.
*.Y -I:,.,~,~$>
-.
FIGURE14 – PROGRAMMING MODEL OF
THE MICROPROCESSINGUNIT
Program Counter – The program count~$&~?:’&t&o byte
(16 bits) register that points to the curre~~,”w~$m address.
,+$‘,~,i
Accumulator A
Stack Pointer – The stack pon~*i~%,;&o byte register
that contains the address of the ne&,,a$ilable location in an
external push-down/pop-up st$~~$~fs stack is normally a
random access Read/Write,,,%b*~.#’’that may have any loca-
tion (address) that is conV@ieJ~t. In those applications that
require storage of inf@~atidB’ In the stack when power is
lost, the stack muskl~~~~,.v,o,,latile.
$:.,,,
~?,
..
Index RWis~~~~~$%e index register is a two byte register
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that is used x~i$~$?data or a sixteen bit memory address for
the lnde&& &&e
;8 _,*_.:,.
{.. .. . ^:$.....^,\.^,.^,:+L.\:!!i,
of memory addressing.
Aq~$#~ators
– The MPU contains two 8-bit ac-
cwuktprs that are used to hold operands and results from
a~~{~~metic logic unit (ALU).
...
Condition Code Register – The condition code register in-
dicates the results of an Arithmetic Logic Unit operation:
Negative (N), Zero (Z), Overflow (V), Carry from bit 7 (C),
and half carry from bit 3 (H). These bits of the Condition
Code Register are used as testable conditions for the condi-
tional branch instructions. Bit 4 is the interrupt mask bit (l).
The unused bits of the Condition Code Register (b6 and b7)
are ones.
Accumulator B
Index Register
Pc
Program Counter
0
SP
Stack Pointer
7
llt
m
w^INZVC
o
Condition
Registar
Code
Carrv (From Bit 7)
r ;:::t ^{II -}
zero ^Overflow
Half Carrv (From Bit 3)
—.
@
MOTOROLA
Semiconductor Products Inc.
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