Hardware manual

Rev. 3.0, 09/98, page 53 of 361
Section 3 MCU Operating Modes and Address Space
3.1 Overview
3.1.1 Mode Selection
The H8/338 Series operates in three modes numbered 1, 2, and 3. The mode is selected by the
inputs at the mode pins (MD
1
and MD
0
) when the chip comes out of a reset. See table 3.1.
The ROMless versions of the H8/338 Series (HD6413388, HD6413378) can be used only in mode
1 (expanded mode with on-chip ROM disabled).
Table 3.1 Operating Modes
Mode MD1 MD0 Address space On-chip ROM On-chip RAM
Mode 0 Low Low 
Mode 1 Low High Expanded Disabled Enabled
*
Mode 2 High Low Expanded Enabled Enabled
*
Mode 3 High High Single-chip 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 64K bytes.
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 H8/338 Series. Avoid setting the mode pins to mode 0.
In addition, the mode pins must not be changed during MCU operation.