Rabel Talpur:12BME#025
 40-pin
chip
 Developed by Motorola in 1975
 16 address lines and 8 data lines
 Used only +5V
 Registers
 Arithmetic
and Logic Unit
 Control Unit
 Program Counter
 Stack Pointer
 Status Flags
A
B
IX
PC
SP
CC
Accumulator A
Accumulator B
Index register X
Program counter
Stack pointer
Condition code register
 The
micro processor unit contains 2
accumulators designed ACCA and ACCB.
 Each
accumulators is 8 bits (one byte) long
and is used to hold operands and data from
the arithmetic logic unit
 The
index register (x) is a 16 bit (2 byte)
register which is primarily used to store a
memory address in the indexed mode of
memory addressing.
 The
index register may be decremented,
incremented and stored.
 The
condition code register is an 8 bit
register. each individual bit may get set or
cleared from of an instruction.
 Each instruction effects the condition code
register differently.
 The primary use of this register is execution
of the conditional branch instruction.
 ALU
is a digital circuit that performs integer
arithmetic and logical operations.
 It is fundamental building block of central
processing unit.
 It
is a component of central processing unit
which direct the operation of processor.
 It control communication and co-ordination
between i/o devices.
 It reads interrupts instructions and
determine the sequence for processing the
data.
 It performs the task of fetching, decoding,
managing, execution and finally storing
results.
 Program
counter contain the address of the
memory containing the next instruction to be
executed.
 It is incremented automatically after each
instruction
 In 6800, it is a 16 bits register
 Used
to point to the memory location where
all registers will be saved when an interrupt
occurs
 It is a 16 bit register, contain an address of a
memory
 16
address wires =it can address 216 memory
locations
 It is an 8 bit microprocessor => 8 data bits
 Speed
up to 4 MHZ
 Architecture
S.No
6800
8085
1
It has two
accumulators
Only one
accumulator is
present
2
Uses frequency 1 MHz uses frequency from
3 to 5 MHz
3
It has index register
No index register is
present
4
Has 3 interrupts
(IRQ,NMI,SWI)
Has five interrupts
(Trap, RST 7.5,RST
6.5, RST 7.5, INTR)
BLOCK DIAGRAM OF 6800
INTERRUPTS
 INTERRUPTS
 IRO
IRQ
 mask
able interrupt. When the interrupt
occurs the program counter, index register,
accumulators and condition code registers
are stored in the stack, the further interrupts
are disabled and the processor jumps to
memory location address of which is stored
in memory FFF8h - FFF9h. To return from the
interrupt the processing routine should use
RTI instruction. This interrupt can be
enabled/disabled using CLI/SEI instructions.
NMI
NMI
non-maskable interrupt. When the interrupt
occurs the program counter, index register,
accumulators and condition code registers are
stored in the stack, the further interrupts are
disabled and the processor jumps to memory
location address of which is stored in memory
FFFCh - FFFDh. To return from the interrupt the
processing routine should use RTI instruction.
This interrupt can not be disabled.
SWI
SWI
 software
interrupt. This interrupt can be only
invoked from the program. When the
interrupt occurs the processor stores the
program counter, index register,
accumulators and condition code registers in
the stack, disables the further interrupts and
jumps to memory location address of which
is stored in memory FFFAh - FFFBh. To return
from the interrupt the processing routine
should use RTI instruction. This interrupt can
not be disabled.
I/O ports
 None.
REGISTERS
 Accumulator
A (ACCA) is an 8-bit register
used for arithmetic and logic operations.
 Accumulator B (ACCB) is an 8-bit register
used for arithmetic and logic operations.
 Index
(IX) is a 16-bit register usually used for
temporary storage or as an index when
indexed addressing is used.
 Program counter (PC) is a 16-bit register.
 Stack pointer (SP) is a 16-bit register.
Condition code register contains the following
flags:
Condition code register contains the following
flags:
 Half carry (H) - set if there was a carry from bit
3 to bit 4 of the result when the result was
calculated.
 Interrupt mask (I) - set if the IRQ interrupt is
disabled.
 Negative (N) - set if the most significant bit of
the result is set.
 Zero (Z) - set if the result is zero.
 Overflow (V) - set if there was an overflow
during last result calculation.
 Carry (C) - set if there was a carry from the bit 7
during last result calculation.

 Instruction
Set
 6800 instruction set consists of 72
instructions:
 Data moving instructions.
 Arithmetic - add, subtract, negate,
increment, decrement and compare.
 Logic - AND, OR, exclusive OR, complement
and shift/rotate.
 Control transfer - conditional, unconditional,
call subroutine and return from subroutine.
 Other - clear/set condition flags, bit test,
stack operations, software interrupt, etc.
 Addressing
modes
 Implied - the data value/data address is
implicitly associated with the instruction.
 Accumulator - the instruction implies that
the data is one of the accumulator registers.
 Immediate - 8-bit or 16-bit data is provided
in the instruction.
MEMORY
 MEMORY
 Program,
size is 64 KB. data and stack
memories occupy the same memory space.
The total addressable memory .
DATAMEMORY
MEMORY
 DATA

data can be anywhere in memory space.
PROGRAM MEMORY
 program
can be located anywhere in
memory. Jump and subroutine call
instructions can be used to jump anywhere in
memory.
 STACK
MEMORY
STACK
MEMORY
 stack
can be placed anywhere in memory
space.
RESERVED MEMORY LOCATION
 FFF8h
- FFF9h: Pointer to IRQ interruptprocessing routine.
 FFFAh - FFFBh: Pointer to software interruptprocessing routine.
 FFFCh
- FFFDh: Pointer to NMI interruptprocessing routine.
 FFFEh - FFFFh: Pointer to RESET handling
code.
 Some memory addresses may be reserved for
memory mapped I/O as the processor doesn't
have hardware I/O capability.
INSTRUCTION SET MOTOROLA 6800
PRESENTED
BY: MURK
SALEEM
12BME19
Group of instructions
executed by
microprocessor is
called as:
“INSTRUCTION SET”.
Motorola-6800 has 72
instructions.
1.ARITHMETIC
INSTRUCTIONS
OPERATION
OPCODE/
MNEMONICS
ALL REGISTER
LABELS REFER
TO CONTENTS
1.Addition
ADDA
A+MA
ADDB
B+MB
2.Add
Accumulators
ABA
A+BA
3.Add With Carry
ADCA
A+M+C
4.Compliment
2`s (Negative)
NEG
00-MM
NEG A
00-AA
NEG B
00-BB
SUB A
A-MA
SUB B
B-MB
SB A
A-BA
5.Subtract
6.Subtract
Accumulators
Two`s
compliment
arithmetic is used
in “MP6800”
which allow us to
take the 2’s
compliment of a
number.
The negative
instruction allows
us to operate on a
byte in memory
without first
fetching the
operand from
memory. In the
past, we have
loaded the
operand,
performed
operation and
then stored the
new operand
2. DATA HANDLING
INSTRUCTIONS:
OPERATION
1.Clear
2.Decrement
3.Increment
4.Load
Accumulator
5.Rotate Left
OPCODES/
NMEMONICS
ALL REGISTER
LABELS REFER
TO CONTENTS
CLR
00M
CLR A
00A
CLR B
00B
DEC
M-1M
DEC A
A-1A
DEC B
B-1B
INC
M+1M
INC A
A+1A
INC B
B+1B
LDAA
MA
LDAB
MB
ROL
M
ROL A
A
ROL B
B
“CLEAR”
instruction
allows us to
clear a memory
or either
accumulator. In
the past, we
have cleared
bytes of first
clearing the
accumulator
then storing the
result in the
proper memory
location.
However, the
CLR instruction
allows us to
clear a memory
location with a
single
instruction.
OPERATION
OPCODES/
NMEMONICS
ALL REGISTER
LABELS REFER
TO CONTENTS
6.Rotate Right
ROR
M
ROR A
A
ROR B
B
STA A
AM
7.Store
Accumulator
8. Transfer
Accumulator
STA B
BM
TAB
AB
TBA
BA
“TRANSFER
ACCUMULATOR” copies
the contents of
accumulator A or B.
After this instruction is
executed, the number
originally present in
any accumulator(eg: A)
will be in both
accumulators.
3. LOGIC
INSTRUCTIONS:
OPERATION
OPCODES/
NMEMONICS
ALL REGISTER LABELS
REFER TO CONTENTS
1. And
AND A
A.MA
AND B
B.MB
2.Compliment,1`s
COM
M M
COM A
A A
3.X-OR
4.OR
EOR A
A (+) M
EOR B
B (+) M
OR A
A+MA
OR B
B+MB
4. DATA TEST
INSTRUCTIONS:
OPERATION
OPCODES/ NMEMONICS
ALL REGISTER LABELS
REFER TO CONTENTS
1. Bit Test
BIT A
A.M
BIT B
B.M
CMP A
A—M
CMP B
B—M
CBA
A—B
2.Compare
3.Compare Accumulators
“BIT TEST” this instruction is very similar to the AND instructions. In
both cases, the contents of the specified accumulator are ANDed with
the contents of the selected memory location. The difference is that
with the bit test instruction no logical product is produced. Neither the
contents of the accumulator nor memory are altered in any way.
However condition code are affected just as if the AND operation had
taken place. Consider BITA instruction, when executed, A is ANDed
with M. If result is 0000, the Z register is set. Otherwise, the Z register
is cleared.
5. INDEX
REGISTER AND
STACK POINTER
INSTRUCTIONS:
The index and stack pointer are 16-bit
registers. That allow us to control the
operation of these registers. Because of
the 16-bit format, the load, store, and
compare instructions are slightly
different.
OPERATION
OPRANDS/
NMEMONICS
ALL REGISTER LABELS
REFER TO CONTENTS
1.Compare Index Reg.
CPX
(𝑋𝐻 /𝑋𝐿 )—(M/M+1)
2.Decrement Index Register DEX
X-1X
3.Decrement Stack Pointer
DES
SP-1SP
4. Increment Stack Pointer
INS
SP+1SP
5.Increment Index Register
INX
X+1X
The “COMPARE REGISTER” instruction allows us to compare the 16-bit
number in the index register with any two consecutive bytes in memory.
(as index register hold two bytes). The higher byte is defined as “𝑿𝑯 ”
while the lower byte is defined as “𝑿𝑳 ”. When the CPX instruction is
executed, “𝑿𝑯 ” is compared with 8-byte in the specified memory
location (M) and “𝑿𝑳 ” is compared with byte immediately following the
specified memory location (M+1).
6.BRANCH INSTRUCTIONS:
Condition code register contains the following flags:
Half carry (H) - set if there was a carry from bit 3 to bit
4 of the result when the result was calculated.
Interrupt mask (I) - set if the IRQ interrupt is disabled.
Negative (N) - set if the most significant bit of the
result is set.
Zero (Z) - set if the result is zero.
Overflow (V) - set if there was an overflow during last
result calculation.
Carry (C) - set if there was a carry from the bit 7 during
last result calculation.
OPERATION
OPCODE/
NMEMONICS
ALL REGISTER LABELS
REFER TO CONTENTS
1.Branch Always
BRA
NONE
2.Branch If Clear
BCC
C=0
3.Branch If Carry Set
BCS
C=1
4.Branch If Minus
BMI
N=1
5.Branch If Plus
BPL
N=0
6.Branch If Over-Flow Set
BVS
V=1
7.Branch If Over-Flow
Clear
BVC
V=0
7. CONDITION CODE REGISTER:-
The 6800 uses these instructions in order to
direct access the condition codes.
OPERATION
OPCODES/ NMEMONICS
ALL REGISTER LABELS
REFER TO CONTENTS
1.Clear Carry
CLC
0C
2.Clear Interrupt Mask
CLI
0I
3.Clear Over-Flow
CLV
0V
4.Set Carry
SEC
1C
5.Set Interrupt Mask
SEI
1I
6.Set Over-Flow
SEV
1V