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CHAPTER 3 CPU
I Mode pins
The MB89470 series devices are single-chip mode devices. The mode pins (MODE) must be tied to VSS.
Do not change the mode pin settings, even after the reset has been completed.
I Mode fetch
When the CPU wakes up from a reset, it reads the mode data and reset vector from internal ROM.
G Mode data (address: FFFD
H)
Always set the mode to "00H" (single-chip mode).
G Reset vector (address: FFFE
H (upper), FFFFH (lower))
Contains the address where execution is to start after completion of the reset. The CPU starts executing
instructions from the address contained in the reset vector.
I Oscillation stabilization wait reset state
The reset operation for a power-on reset or external reset in stop mode starts after the oscillation
stabilization wait time determined by the time-based timer. If the external reset input has not been released
when the wait time completes, the reset operation does not start until the external reset is released.
As the oscillation stabilization wait time is also required when an external clock is used, a reset requires
that the external clock is input.
The main clock oscillation stabilization wait time is timed by the timebase timer.
I Effect of reset on RAM contents
The contents of RAM are unchanged before and after a reset other than power-on reset. If an external reset
is input close to a write timing, however, the contents of the write address cannot be assured. For this
reason, all RAM locations being used should be initialized following reset.
I Regulator recovery time
MB89P475 series contains an on-chip voltage regulator for the internal 3V circuits. In power-down mode
or in the stop mode, the internal voltage regulator is turned off to minimize power consumption. The
Regulator Recovery Time is the the time for the internal voltage regulator to resume normal operation.
The Regulator Recovery Time is 20
second long, and it is required only in MB89P475.
I Power-on stabilization time
When power-on, the on-chip voltage regulator requires a stabilization time in additional to the oscillation
stabilization time. This additional wait time is called power-on Stabilization Time. The external power
supply voltage must reach the mininum operation voltage within the Power-On stabilization time. For
product without regulator, it is selectable.
The Power-On Stabilization Time is required in MB89P475 and selectable in MB89475. It depends on the
oscillating clock, and it is 217/FCH long (FCH is the main clock operating frequency).