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CHAPTER 4 RESET
4.3 External Reset Pin
4.3
External Reset Pin
The external reset pin (RST pin), dedicated to reset input pin, generates an internal
reset in response to input of the "L" level signal. MB90335 series are reset in sync with
the CPU operating clock, except for external pin in asynchronous (generated through
ports and so on), which change to the reset state.
■ Block Diagram of External Reset Pin
Figure 4.3-1 shows the block diagram of the generation of the internal reset.
RST
Pin
HCLK : Oscillation clock
Note:
To protect the memory from destruction by a reset during write operation, the RST pin input is
accepted with a cycle which does not cause the memory to be destroyed.
Also, the clock is required to initialize the internal circuits. In particular, when using an external clock,
the clock must be input during input of the reset.
116
Figure 4.3-1 Block Diagram of Internal Reset Generation
P-ch
N-ch
Input buffer
FUJITSU MICROELECTRONICS LIMITED
CPU operation clock
(PLL frequency multiplication circuit,
divided-by-two of HCLK)
Synchronous
circuit
MB90335 Series
CPU
Peripheral
function
I/O port
etc.
CM44-10137-6E
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