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CHAPTER 3 CPU
3.6.2
External Reset Pin
The external reset pin (RST pin) is a reset input pin. Input of an external Low level
generates a reset factor. MB90895 series starts the reset operation in synchronization
between the CPU and clock.
I Block Diagram of External Reset Pin
RST
Pin
HCLK Oscillation colck
Notes:
• To prevent memory from being broken due to a reset during writing to memory, a Low
level is input to the RST pin in a machine cycle in which memory is not broken.
• The CPU operation clock is required to initialize internal circuits. During operation using
an external clock, in particular, the reset signal and CPU operation clock signal must be
input.
100
Figure 3.6-2 Block Diagram of External Reset Pin
Input buffer
Pch
Nch
CPU operating clock (PLL multiplier circuit,
2-frequency division of HCLK)
Synchronization
Internal reset siganal
of circuit
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