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M37905M6C-XXXFP

16 BIT CMOS MICROCOMPUTER

Mitsumi 

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MITSUBISHI MICROCOMPUTERS

M37905M4C-XXXFP, M37905M4C-XXXSP

M37905M6C-XXXFP, M37905M6C-XXXSP

M37905M8C-XXXFP, M37905M8C-XXXSP

16-BIT CMOS MICROCOMPUTER

CENTRAL PROCESSING UNIT (CPU)

The CPU has 13 registers and is shown in Figure 4. Each of these

registers is described below.

ACCUMULATOR A (A)

Accumulator A is the main register of the microcomputer. It consists

of 16 bits and the low-order 8 bits can be used separately. Data

length flag m determines whether the register is used as 16-bit reg-

ister or as 8-bit register. It is used as a 16-bit register when flag m is

“0” and as an 8-bit register when flag m is “1”. Flag m is a part of the

processor status register (PS) which is described later.

Data operations such as calculations, data transfer, input/output,

etc., are executed mainly through accumulator A.

ACCUMULATOR B (B)

Accumulator B has the same functions as accumulator A, but the use

of accumulator B requires more instruction bytes and execution

cycles than accumulator A.

ACCUMULATOR E

Accumulator E is a 32-bit register and consists of accumulator A

(low-order 16 bits) and accumulator B (high-order 16 bits). It is used

for 32-bit data processing.

INDEX REGISTER X (X)

Index register X consists of 16 bits and the low-order 8 bits can be

used separately. Index register length flag x determines whether the

register is used as 16-bit register or as 8-bit register. It is used as a

16-bit register when flag x is “0” and as an 8-bit register when flag x

is “1”. Flag x is a part of the processor status register (PS) which is

described later.

In index addressing modes in which register X is used as the index

register, the contents of this address are added to obtain the real ad-

dress.

Index register X functions as a pointer register which indicates an

address of data table in instructions MVP, MVN, RMPA (Repeat

MultiPly and Accumulate).

INDEX REGISTER Y (Y)

Index register Y consists of 16 bits and the low-order 8 bits can be

used separately. The index register length flag x determines whether

the register is used as 16-bit register or as 8-bit register. It is used as

a 16-bit register when flag x is “0” and as an 8-bit register when flag

x is “1”. Flag x is a part of the processor status register (PS) which is

described later.

In index addressing modes in which register Y is used as the index

register, the contents of this address are added to obtain the real ad-

dress.

Index register Y functions as a pointer register which indicates an

address of data table in instructions MVP, MVN, RMPA (Repeat

MultiPly and Accumulate).

15

31

7

PG

7

DT

Accumulator B

Accumulator A

7

0 15

7

0

BH

BL

AH

AL

0

Accumulator E

15

7

0

AH

AL

15

7

0

BH

BL

15

XH

7

0

XL

Index register X

15

7

0

YH

YL

Index register Y

15

0

S

Program bank register PG

15

0

Stack pointer S

0

0

Data bank register DT

15

PC

DPR0 to DPR3

Program counter PC

0

Direct page registers DPR0 to DPR3

15

7

0

0 0 0 0 0 IPL2 IPL1 IPL0 N V m x D I Z C Processor status register PS

Carry flag

Zero flag

Interrupt disable flag

Decimal mode flag

Index register length flag

Data length flag

Overflow flag

Negative flag

Processor interrupt priority level IPL

Fig. 4 Register structure

11

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