HD6433640 HITACHI [Hitachi Semiconductor], HD6433640 Datasheet - Page 60

• Manufacturer Part Number: HD6433640
• Description: H8/3644 Series Hardware Manual
• Manufacturer: HITACHI [Hitachi Semiconductor]

2.9
2.9.1
1. Access to empty areas
2. Access to internal I/O registers
Byte size instructions should therefore be used when transferring data to or from I/O registers
other than the on-chip ROM and RAM areas. Figure 2.17 shows the data size and number of states
in which on-chip peripheral modules can be accessed.
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The address space of the H8/300L CPU includes empty areas in addition to the RAM,
registers, and ROM areas available to the user. If these empty areas are mistakenly accessed by
an application program, the following results will occur.
Data transfer from CPU to empty area:
Data transfer from empty area to CPU:
Internal data transfer to or from on-chip modules other than the ROM and RAM areas makes
use of an 8-bit data width. If word access is attempted to these areas, the following results will
occur.
Word access from CPU to I/O register area:
Word access from I/O register to CPU:
The transferred data will be lost. This action may also cause the CPU to misoperate.
Unpredictable data is transferred.
Upper byte: Will be written to I/O register.
Lower byte: Transferred data will be lost.
Upper byte: Will be written to upper part of CPU register.
Lower byte: Unpredictable data will be written to lower part of CPU register.
Application Notes
Notes on Data Access