W78LE54 Datasheet, PDF (8/22 Pages) Winbond – 8-BIT MTP MICROCONTROLLER

Preliminary W78LE54
WIDL
IDLE
OSC
1/12
ENW
EXTERNAL
RESET
PRESCALER
14-BIT TIMER
CLEAR
INTERNAL
RESET
Watchdog Timer Block Diagram
CLRW
Typical Watch-Dog time-out period when OSC = 20 MHz
PS2 PS1 PS0
00 0
00 1
01 0
01 1
10 0
10 1
11 0
11 1
WATCHDOG TIME-OUT PERIOD
19.66 mS
39.32 mS
78.64 mS
157.28 ms
314.57 mS
629.14 mS
1.25 S
2.50 S
Clock
The W78LE54 is designed to be used with either a crystal oscillator or an external clock. Internally,
the clock is divided by two before it is used. This makes the W78LE54 relatively insensitive to duty
cycle variations in the clock. The W78LE54 incorporates a built-in crystal oscillator. To make the
oscillator work, a crystal must be connected across pins XTAL1 and XTAL2. In addition, a load
capacitor must be connected from each pin to ground. An external clock source should be connected
to pin XTAL1. Pin XTAL2 should be left unconnected. The XTAL1 input is a CMOS-type input, as
required by the crystal oscillator.
Power Management
Idle Mode
The idle mode is entered by setting the IDL bit in the PCON register. In the idle mode, the internal
clock to the processor is stopped. The peripherals and the interrupt logic continue to be clocked. The
processor will exit idle mode when either an interrupt or a reset occurs.
Power-down Mode
When the PD bit of the PCON register is set, the processor enters the power-down mode. In this
mode all of the clocks are stopped, including the oscillator. The only way to exit power-down mode is
by a reset.
-8-