FUJITSU Semiconductor Controller MB89950/950A - Manual (Page 59)

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CHAPTER 3 CPU
3.5.1 External Reset Pin
Inputting an "L" level to the external reset pin generates a reset. If products are set to
with the reset output (optional), the pin outputs an "L" level depending on internal reset
sources.
■ Block diagram of external reset pin
The external reset pin (RST) on products with the reset output is a hysteresis input type and N-ch open-
drain output type with a pull-up resistor.
The external reset pin on products without a reset output option is only for the reset input.
Figure 3.5-1 "Block diagram of external reset pin" shows the block diagram of the external reset pin.
Figure 3.5-1 Block diagram of external reset pin
■ External reset pin functions
Inputting an "L" level to the external reset pin (RST) generates an internal reset signal.
When selecting products with reset output (option setting), the pin outputs an "L" level depending on
internal reset sources or during the oscillation stabilization delay time due to an external reset. Software
reset, watchdog reset, and power-on reset are classed as internal reset sources.
Note:
The external reset input accepts asynchronous with the internal clock. Therefore, initialization of the
internal circuit requires a clock. Especially when an external clock is used, a clock is needed to be input
at the reset.
P-ch
N-ch
RST
Pin
Pull-up resistor
Approx. 50 k (5.0V)
Option
With reset output
Without reset output
Internal reset source
Input buffer
Internal reset signal