Section 3 MCU Operating Modes and Address Space
3.1
Overview
3.1.1
Mode Selection
The H8/3397 and H8/3337 Series operate in three modes numbered 1, 2, and 3. The mode is
selected by the inputs at the mode pins (MD1 and MD0). See table 3.1.
Table 3.1 Operating Modes
Mode
MD1
Low
Low
High
High
MD0
Low
High
Low
High
Address Space
—
On-Chip ROM
—
On-chip RAM
—
Mode 0
Mode 1
Mode 2
Mode 3
Expanded
Expanded
Single-chip
Disabled
Enabled
Enabled
Enabled*
Enabled*
Enabled
Note: * If the RAME bit in the system control register (SYSCR) is cleared to 0, off-chip memory can
be accessed instead.
Modes 1 and 2 are expanded modes that permit access to off-chip memory and peripheral devices.
The maximum address space supported by these externally expanded modes is 64 kbytes.
In mode 3 (single-chip mode), only on-chip ROM and RAM and the on-chip register field are
used. All ports are available for general-purpose input and output.
Mode 0 is inoperative in the H8/3397 and H8/3337 Series. Avoid setting the mode pins to mode 0.
Avoid setting the mode pins to mode 0, and do not change the mode pin settings while the chip is
operating.
3.1.2
Mode and System Control Registers
Table 3.2 lists the registers related to the chip’s operating mode: the system control register
(SYSCR) and mode control register (MDCR). The mode control register indicates the inputs to the
mode pins MD1 and MD0.
Table 3.2 Mode and System Control Registers
Name
Abbreviation
SYSCR
Read/Write
Address
H'FFC4
H'FFC5
System control register
Mode control register
R/W
R
MDCR
63
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