Hardware manual

Rev. 3.0, 09/98, page 271 of 361
15.4.4 Application Note
1. The I/O ports retain their current states in the software standby mode. If a port is in the High
output state, the current dissipation caused by the High output current is not reduced.
2. When software standby mode is entered under condition (a) or (b) below, current dissipation is
higher (I
CC
= 100 to 300 µA) than normal in standby mode.
(a) In single-chip mode (mode 3): when software standby mode is entered by executing an
instruction stored in on-chip ROM, after even one instruction not stored in on-chip ROM
has been fetched (e.g. from on-chip RAM).
(b) In expanded mode with on-chip ROM enabled (mode 2): when software standby mode is
entered by executing an instruction stored in on-chip ROM, after even one instruction not
stored in on-chip ROM has been fetched (e.g. from external memory or on-chip RAM).
Note that the H8/300 CPU pre-fetches instructions. If an instruction stored in the last two bytes
of on-chip ROM is executed, the contents of the next two bytes, not in on-chip ROM, will be
fetched as the next instruction.
This problem does not occur in expanded mode when on-chip ROM is disabled (mode 1).
In hardware standby mode there is no additional current dissipation, regardless of the conditions
when hardware standby mode is entered.