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M37640E8

Single-Chip 8-BIT CMOS Microcontroller M37640E8-XXXFP Specification

MITSUBISHI ELECTRIC  

Mitsubishi Microcomputer

7600 Series

M37640E8-XXXF Preliminary Specification

2 Functional Description

2.1 Central Processing Unit

The central processing unit (CPU) has six registers:

• Accumulator (A)

• Index Register X (X)

• Index Register Y (Y)

• Stack Pointer (S)

• Processor Status Register (PS)

• Program Counter (PC)

2.1.1 Register Structure

7

Accumulator

0

7

0

Index Register X

7

Index Register Y

0

7

Stack Pointer

0

15

7

PCH

PCL

0

Program Counter

7 N V T B D I Z C 0 Processor Status Register

Carry Flag (bit 0)

Zero Flag (bit 1)

Interrupt Disable Flag (bit 2)

Decimal Mode Flag (bit 3)

Break Flag (bit 4)

Index X Mode Flag (bit 5)

Overflow Flag (bit 6)

Negative Flag (bit 7)

Figure 2-1. Register Structure

Five of the CPU registers are 8-bit registers. These are the Accumulator (A), Index register X (X),

Index register Y (Y), Stack pointer (S), and the Processor Status register (PS).

The Program counter (PC) is a 16-bit register consisting of two 8-bit registers (PCH and PCL) (see

Figure 2-1.).

After a hardware reset, bit 2 (the I flag) of the PS is set high and the values at the addresses FFFA16

and FFFB16 are stored in the PC, but the values of the other bits of the PS and the other registers are

undefined. Initialization of undefined registers may be necessary for some programs.

2.1.2 Accumulator (A)

The accumulator is the main register of the microcomputer. Data operations such as data transfer, input/

output, and so forth, are executed mainly through the accumulator.

Central Processing Unit

7/9/98

2-3

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