P80C557E4EFB NXP Semiconductors, P80C557E4EFB Datasheet - Page 28

• Manufacturer Part Number: P80C557E4EFB
• Manufacturer: NXP Semiconductors

Specifications of P80C557E4EFB

• Cpu Family: 80C
• Device Core: 80C51
• Device Core Size: 8b
• Frequency (max): 16MHz
• Interface Type: I2C/UART
• Program Memory Type: ROMLess
• Program Memory Size: Not Required
• Total Internal Ram Size: 1KB
• # I/os (max): 40
• Number Of Timers - General Purpose: 3
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 4.5V
• On-chip Adc: 8-chx10-bit
• Instruction Set Architecture: CISC
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 80
• Package Type: PQFP
• Lead Free Status / Rohs Status: Compliant

Philips Semiconductors
6.8 Watchdog Timer T3
In addition to Timer T2 and the standard timers, a watchdog timer
(T3) consisting of an 11-bit prescaler and an 8-bit timer is also
incorporated (see Figure 27).
The timer is incremented every 1.5 ms, derived from the system
clock frequency of 16 MHz by the following:
When a timer overflow occurs, the microcontroller is reset and a
reset output pulse is generated at pin RSTOUT. Also the PLL control
register is reset.
To prevent a system reset the timer must be reloaded in time by the
application software. If the processor suffers a hardware/software
malfunction, the software will fail to reload the timer. This failure will
1999 Mar 02
Single-chip 8-bit microcontroller
f
timer
f
12
CLK
f
CLK
/12
EW
2048
Write T3
Prescaler
Clear
(11-bit)
Figure 27. Watchdog timer.
PCON.4
Internal Bus
Internal Bus
28
LOAD LOADEN
Timer T3
Clear
(8-bit)
WLE
P83C557E4/P80C557E4/P89C557E4
In the Idle state the watchdog timer and reset circuitry remain active.
produce a reset upon overflow thus preventing the processor
running out of control.
The watchdog timer can only be reloaded if the condition flag
WLE = PCON.4 has been previously set by software.
At the moment the counter is loaded the condition flag is
automatically cleared.
The time interval between the timer’s reloading and the occurrence
of a reset depends on the reloaded value. For example, this may
range from 1.5 ms to 0.375 s when using an oscillator frequency of
16 MHz.
The watchdog timer is controlled by the watchdog enable pin (EW).
A LOW level enables the watchdog timer and disables the
Power-down Mode. A HIGH level disables the watchdog timer and
enables the Power-down Mode.
LOADEN
to reset circuitry (see Figure 46)
PD
PCON.1
Product specification