M16CSLASH62M datasheet(41/615 Pages) RENESAS

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Mitsubishi microcomputers

M16C / 62A Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Software Reset

1-22

Software Reset

Writing “1” to bit 3 of the processor mode register 0 (address 000416) applies a (software) reset to the

microcomputer. A software reset has the same effect as a hardware reset. The contents of internal RAM

are preserved.

Software Reset

Processor Mode

(1) Types of Processor Mode

One of three processor modes can be selected: single-chip mode, memory expansion mode, and micro-

processor mode. The functions of some pins, the memory map, and the access space differ according to

the selected processor mode.

• Single-chip mode

In single-chip mode, only internal memory space (SFR, internal RAM, and internal ROM) can be

accessed. However, after the reset has been released and the operation of shifting from the micropro-

cessor mode has started (“H” applied to the CNVSS pin), the internal ROM area cannot be accessed

even if the CPU shifts to the single-chip mode.

Ports P0 to P10 can be used as programmable I/O ports or as I/O ports for the internal peripheral

functions.

• Memory expansion mode

In memory expansion mode, external memory can be accessed in addition to the internal memory

space (SFR, internal RAM, and internal ROM). However, after the reset has been released and the

operation of shifting from the microprocessor mode has started (“H” applied to the CNVSS pin), the

internal ROM area cannot be accessed even if the CPU shifts to the memory expansion mode.

In this mode, some of the pins function as the address bus, the data bus, and as control signals. The

number of pins assigned to these functions depends on the bus and register settings. (See “Bus

Settings” for details.)

• Microprocessor mode

In microprocessor mode, the SFR, internal RAM, and external memory space can be accessed. The

internal ROM area cannot be accessed.

In this mode, some of the pins function as the address bus, the data bus, and as control signals. The

number of pins assigned to these functions depends on the bus width and register settings. (See “Bus

Settings” for details.)

(2) Setting Processor Modes

The processor mode is set using the CNVSS pin and the processor mode bits (bits 1 and 0 at address

000416). Do not set the processor mode bits to “102”.

Regardless of the level of the CNVSS pin, changing the processor mode bits selects the mode. Therefore,

never change the processor mode bits when changing the contents of other bits. Do not change the

processor mode bits simultaneously with other bits when changing the processor mode bits “012” or

“112”. Change the processor mode bits after changing the other bits. Also do not attempt to shift to or from

the microprocessor mode within the program stored in the internal ROM area.

• Applying VSS to CNVSS pin

The microcomputer begins operation in single-chip mode after being reset. Memory expansion mode

is selected by writing “012” to the processor mode bits.

• Applying VCC to CNVSS pin

The microcomputer starts to operate in microprocessor mode after being reset.

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