SM8521 Datasheet, PDF (23/56 Pages) Sharp Electrionic Components – 8-Bit Single-Chip Microcomputer

SM8521
Hardware Reset
The hardware reset is an initial function for SM8521
system and comes from the following sources.
• External reset
If the RESETB pin is applied to Low level in
SM8521 operating, the hardware resets.
• Watchdog timer overflow
While watchdog timer overflows, the hardware
resets.
The above 2 hardware reset sources initializate the
system.
OPERATING EXPLANATIONS
• Hardware reset operation
When the SM8521 is operating, a built-in pull-up
resistor keeps the RESETB pin at High level. If
external circuit (like as reset IC etc.) applies Low
level voltage to RESETB pin, the SM8521 is reset
by hardware after approximately two instruction
cycles. To ensure hardware reset execution keeps
the RESETB pin at Low level over two instruction
cycles of system clock.
The pin back to High level from Low level starts the
warming up counter built-in SM8521. When the
counter overflows, about 2¹⁸ x main-clock leaves its
hardware reset state and begins the program
execution from the instruction at address 1020H. In
the warming up interval, SM8521 is in HALT mode
state.
Same as watchdog timer overflow case, the CPU
leaves the hardware reset behind warming up period.
Interrupt Function
The SM8521 supports 10 interrupt sources.
In these interrupts, watchdog timer and illegal
instruction trap interrupts belong to non-maskable
interrupts, the others, however, are maskable
interrupts. 10 interrupt sources are shared to
independent interrupt vector respectively, in the
ROM address area between 1000H-101FH. And, the
maskable interrupts are set 8 steps with priority
level.
210
PS0
IM
Interrupt request register
Interrupt enable register
IR0
IE0
0
IR1
IE1
PS1
I
With priority 8 levels
With priority 1 level
WDT (NMI)
Illegal instruction trap
Fig. 10 Interrupt Block Diagram
- 23 -
Interrupt signal
Interrupt process