Address Error; Illegal Instruction Prefetch; Word Data Access At Odd Address; Off-Chip Address Access In Single-Chip Mode - Hitachi H8/500 Series Hardware Manual

4.3 Address Error

There are three causes of address errors:

• Illegal instruction prefetch

• Word data access at odd address

• Off-chip access in single-chip mode
An address error initiates the address error exception-handling sequence. This sequence clears the
T bit of the status register to "0" to disable the trace mode, but does not affect the interrupt mask
level in bits I2 to I0.
4.3.1 Illegal Instruction Prefetch
An attempt to prefetch an instruction from the register field in memory addresses H'FF80 to
H'FFFF causes an address error regardless of the MCU operating mode.
Handling of this address error begins when the prefetch cycle that caused the error has been
completed and execution of the current instruction has also been completed. The program counter
value pushed on the stack is the address of the instruction immediately following the last
instruction executed.
Program code should not be located in addresses H'FF7D to H'FF7F. If the CPU executes an
instruction in these addresses, it will attempt to prefetch the next instruction from the register
field, causing an address error.
4.3.2 Word Data Access at Odd Address
If an attempt is made to access word data starting at an odd address, an address error occurs
regardless of the MCU operating mode. The program counter value pushed on the stack in the
handling of this error is the address of the next instruction (or next but one) after the instruction
that attempted the illegal word access.

4.3.3 Off-Chip Address Access in Single-Chip Mode

In the single-chip mode there is no external memory, so in addition to the address errors described
above, the following two types of address errors can occur.
Access to Addresses H'8000 to H'FB7F: These addresses exist neither in on-chip ROM or RAM
nor in the on-chip register field, so an address error occurs if they are accessed for any purpose:
for instruction prefetch, byte data access, or word data access.
89
Downloaded from Elcodis.com electronic components distributor