P89V51RD2 Philips Semiconductors, P89V51RD2 Datasheet - Page 52

• Manufacturer Part Number: P89V51RD2
• Description: 8-bit 80C51 5 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 12964
Product data
7.10.1 Power-on Reset
At initial power up, the port pins will be in a random state until the oscillator has
started and the internal reset algorithm has weakly pulled all pins HIGH. Powering up
the device without a valid reset could cause the MCU to start executing instructions
from an indeterminate location. Such undefined states may inadvertently corrupt the
code in the flash.
When power is applied to the device, the RST pin must be held HIGH long enough for
the oscillator to start up (usually several milliseconds for a low frequency crystal), in
addition to two machine cycles for a valid power-on reset. An example of a method to
extend the RST signal is to implement a RC circuit by connecting the RST pin to V
through a 10 F capacitor and to V
Figure
ensure the V
time does not exceed 10 milliseconds.
For a low frequency oscillator with slow start-up time the reset signal must be
extended in order to account for the slow start-up time. This method maintains the
necessary relationship between V
indeterminate location, which may cause corruption in the code of the flash. The
power-on detection is designed to work as power-up initially, before the voltage
reaches the brown-out detection level. The POF flag in the PCON register is set to
indicate an initial power-up condition. The POF flag will remain active until cleared by
software. Please refer to the PCON register definition for detail information.
Following reset, the P89V51RD2 will either enter the SoftICE mode (if previously
enabled via ISP command) or attempt to autobaud to the ISP boot loader. If this
autobaud is not successful within about 400 ms, the device will begin execution of the
user code.
Fig 26. Power-on reset circuit.
26. Note that if an RC circuit is being used, provisions should be made to
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rise time does not exceed 1 millisecond and the oscillator start-up
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Rev. 01 — 01 March 2004
8.2 k
10
m
W
F
C 2
C 1
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SS
and RST to avoid programming at an
through an 8.2 k resistor as shown in
XTAL2
XTAL1
RST
8-bit microcontrollers with 80C51 core
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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