MC6800 Datasheet, PDF (22/32 Pages) Motorola, Inc – 8-BIT MICROPROCESSING UNIT (MPU)

L
= BOOLEAN OPERATION
E¹
O+c
1
0+1
1
O+v
1
l+C
1
1+1
1
l-v
1
A+CCR
1
CCR+A
m^{CO ND. COOE REG.}
HI
NZVC
q 00m*
q R****
q .mm
q Ore**
q S.
R
R.
s
*Q.
q **O
s.
q q q^w\*
qq
—.
The M P&%~&$ates on 8-bit binary numbers presented to it
via the..~t~~~?{~us. A given number (byte) may rePresent
eithe&~{~~@:or an instruction to be executed, depending on
w@.@/~,~s encountered in the control program. The Mm
ha$~~tinique instructions, however, it recognizes and takes
actloh on 197 of the 256 possibilities that can occur using an
8-bit word length. This larger number of instructions results
from the fact that many of the executive instructions have
more than one addressing mode.
These addressing modes refer to the manner in which the
program causes the MPU to obtain its instructions and data.
The programmer must have a method for addressing the
MPU’S internal registers and all of the external memory loca-
tions.
Selection of the desired addressing mode is made by the
user as the source statements are written. Translation into
appropriate opcode then depends on the method used. If
manual translation is used, the addressing mode is inherent
in the opcode. For example, the immediate, Direct, Indexed,
and Extended modes may all be used with the ADD instruc-
tion. The proper mode is determined by selecting (hex-
adecimal notation) 8B, 9B, AB, or BB, respectively.
The source statement format includes adequate informa-
tion for the selection if an assembler program is used to
generate the opcode. For instance, the Immediate mode is
selected by the Assembler whenever it encounters the “#”
symbol in the operand field. Similarly, an “X” in the operand
field causes the Indexed mode to be selected. Only the
Relative mode applies to the branch instructions, therefore,
the mnemonic instruction itself is enough for the Assembler
to determine addressing mode.
MOTOROLA
@
Semiconductor Products Inc. ~
22