External-Reset Pin - Fujitsu MB90480 Series Hardware Manual

CHAPTER 4 RESET
4.3

External-Reset Pin

The external-reset pin (pin RST) is a pin dedicated for the input of resets, and it
triggers an internal reset by input of the "L" level. The MB90480/485 series devices
have resets synchronized to the CPU operation clock. However, only external pins
(e.g., ports) change asynchronously to a reset state.
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Block diagram of external-reset pin
Figure 4.3-1 shows the block diagram of internal reset.
Note:
To prevent damage to the memory contents by a reset during writing, input to pin RST is accepted
in a cycle that precludes damage to memory contents.
A clock is required to initialize internal circuits. Input of a clock is required during input of a reset
when an external clock is used for operation.
100
Figure 4.3-1 Block diagram of internal reset
P-ch
RST
Pin
N-ch
Input buffer
HCLK: Oscillation clock
CPU operation clock
(PLL multiplier circuit, clock
of HCLK divided by two)
Synchronization
circuit
I/O ports, etc.
CPU
Peripheral
function