M16C80 Datasheet, PDF (37/358 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/80 SERIES

M16C/80 Group
6. Processor Mode
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.
Carry out a software reset after oscillation of main clock is fully stable.
6. 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 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 changeing 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 is selected bits.
• Applying VCC to CNVSS pin
The microcomputer starts to operate in microprocessor mode after being reset.
Figures 6.1 and 6.2 show the processor mode register 0 and 1.
Figure 6.3 shows the memory maps applicable for each processor modes.
Rev.1.00 Aug. 02, 2005 ^{Page 26} of 329
REJ09B0187-0100