External Reset Pin - Fujitsu MB90420/5 (A) Series Hardware Manual

3.3 External Reset Pin

The external reset pin (RSTX pin) is a reset dedicated pin which generates the internal reset when the "L"
level is input. Only the external pin is reset asynchronously with the CPU operating clock; other pins are
reset synchronously with the CPU operating clock.
n Block diagram of internal reset pin
• Block diagram of internal reset
RSTX
Pch
Pin
Nch
HCLK: Oscillation clock
Note: To prevent damage to memory by a reset during write, the input to the RSTX pin is accepted in a
cycle that does not damage memory. Initialization of the internal circuit requires the clocks. In
particular, when an external clock is used for initialization, the clock must be input at the reset input.
• Block diagram of external reset pin
RSTX
Pch
Pin
Nch
HCLK: Oscillation clock
RESET
Input buffer
Fig. 3.1 Block Diagram of Internal Reset
Input buffer
Fig. 3.2 Block Diagram of External Reset Pin
3-7
CPU operating clock
(PLL multiplier circuit, 2 frequency division of HCLK)
Synchronization circuit Clock synchronization
Internal reset signal
Asynchronization
Internal reset signal