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Section 2 CPU
Rev. 6.00 Sep 12, 2006 page 50 of 526
REJ09B0326-0600
2.9
Application Notes
2.9.1
Notes on Data Access
1. Access to empty areas
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:
The transferred data will be lost. This action may also cause the CPU to misoperate.
Data transfer from empty area to CPU:
Unpredictable data is transferred.
2. Access to internal I/O registers
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:
Upper byte: Will be written to I/O register.
Lower byte: Transferred data will be lost.
Word access from I/O register to CPU:
Upper byte: Will be written to upper part of CPU register.
Lower byte: Unpredictable data will be written to lower part of CPU register.
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.
Summary of Contents for F-ZTAT H8/3642A Series
Page 6: ...Rev 6 00 Sep 12 2006 page iv of xx ...
Page 8: ...Rev 6 00 Sep 12 2006 page vi of xx ...
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Page 124: ...Section 5 Power Down Modes Rev 6 00 Sep 12 2006 page 102 of 526 REJ09B0326 0600 ...
Page 188: ...Section 6 ROM Rev 6 00 Sep 12 2006 page 166 of 526 REJ09B0326 0600 ...
Page 190: ...Section 7 RAM Rev 6 00 Sep 12 2006 page 168 of 526 REJ09B0326 0600 ...
Page 298: ...Section 9 Timers Rev 6 00 Sep 12 2006 page 276 of 526 REJ09B0326 0600 ...
Page 378: ...Section 12 A D Converter Rev 6 00 Sep 12 2006 page 356 of 526 REJ09B0326 0600 ...
Page 446: ...Section 13 Electrical Characteristics Rev 6 00 Sep 12 2006 page 424 of 526 REJ09B0326 0600 ...