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7542 Group
FUNCTIONAL DESCRIPTION
Central Processing Unit (CPU)
The MCU uses the standard 740 family instruction set. Refer to
the table of 740 family addressing modes and machine-language
instructions or the SERIES 740 <SOFTWARE> USER'S MANUAL
for details on each instruction set.
Machine-resident 740 family instructions are as follows:
1. The FST and SLW instructions cannot be used.
2. The MUL and DIV instructions can be used.
3. The WIT instruction can be used.
4. The STP instruction can be used.
Accumulator (A)
The accumulator is an 8-bit register. Data operations such as data
transfer, etc., are executed mainly through the accumulator.
Index register X (X), Index register Y (Y)
Both index register X and index register Y are 8-bit registers. In
the index addressing modes, the value of the OPERAND is added
to the contents of register X or register Y and specifies the real
address.
When the T flag in the processor status register is set to "1", the
value contained in index register X becomes the address for the
second OPERAND.
Fig. 11 740 Family CPU register structure
Rev.3.02
Oct 31, 2006
REJ03B0006-0302
b7
b7
b7
b7
b15
b7
PC
PC
H
b7
N
V
T
B
Page 13 of 134
Stack pointer (S)
The stack pointer is an 8-bit register used during subroutine calls
and interrupts. The stack is used to store the current address data
and processor status when branching to subroutines or interrupt
routines.
The lower eight bits of the stack address are determined by the
contents of the stack pointer. The upper eight bits of the stack ad-
dress are determined by the Stack Page Selection Bit. If the Stack
Page Selection Bit is "0", then the RAM in the zero page is used
as the stack area. If the Stack Page Selection Bit is "1", then RAM
in page 1 is used as the stack area.
The Stack Page Selection Bit is located in the SFR area in the
zero page. Note that the initial value of the Stack Page Selection
Bit varies with each microcomputer type. Also some microcom-
puter types have no Stack Page Selection Bit and the upper eight
bits of the stack address are fixed. The operations of pushing reg-
ister contents onto the stack and popping them from the stack are
shown in Fig. 12.
Program counter (PC)
The program counter is a 16-bit counter consisting of two 8-bit
registers PC
and PC
H
next instruction to be executed.
b0
A
Accumulator
b0
X
Index Register X
b0
Y
Index Register Y
b0
S
Stack Pointer
b0
Program Counter
L
b0
D
I
Z
C
Processor Status Register (PS)
Carry Flag
Zero Flag
Interrupt Disable Flag
Decimal Mode Flag
Break Flag
Index X Mode Flag
Overflow Flag
Negative Flag
. It is used to indicate the address of the
L
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