External Reset Pin - Fujitsu MB90390 Series Hardware Manual

CHAPTER 7 RESETS
7.3

External Reset Pin

The external reset pin (RST pin) is an input pin used exclusively for a reset. Inputting an
"L" level signal generates an internal reset. For the MB90390 series, resets are
generated in synchronization with the CPU operating clock. However, the I/O port pins
are affected by the external reset pin (RST pin) in an asynchronous manner.
■ Block Diagrams of the External Reset Pin
●
Block diagram of internal reset
RST
Pin
Note:
Inputs to the RST are accepted during cycles in which memory is not affected to prevent memory
from being destroyed by a reset during a write operation.
A clock is required to initialize the internal circuit. In particular, an operation with an external clock
requires clock input together with reset input.
130
Figure 7.3-1 Block Diagram of Internal Reset
CPU operating clock
(PLL multiplier circuit with an
HCLK frequency divided by 2)
P-ch
N-ch
Input
buffer
CPU
Synchronization
circuit
Peripheral
functions
I/O port or
other pin