External-Reset Pin - Fujitsu F2MC-16LX 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 MB90470 series devices have
resets synchronized to the CPU operation clock. However, only external pins (e.g.,
ports) change asynchronously to a reset state.
I Block diagram of external-reset pin
Figure 4.3-1 "Block diagram of internal reset" shows the block diagram of internal reset.
RST
Pin
HCLK: Oscillation clock
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.
106
Figure 4.3-1 Block diagram of internal reset
CPU operation clock
(PLL multiplier circuit, clock
of HCLK divided by two)
Pch
Nch
Input buffer
Synchronization
circuit
Peripheral
I/O ports, etc.
CPU
function