P89LV51RD2BA PHILIPS [NXP Semiconductors], P89LV51RD2BA Datasheet - Page 15

• Manufacturer Part Number: P89LV51RD2BA
• Description: 8-bit 80C51 3 V low power 64 kB Flash microcontroller with 1 kB RAM
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
9397 750 14101
Product data
7.1.3 Software reset
7.1.4 Brown-out detect reset
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 during initial power up, 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.
Following a power-on or external reset the P89LV51RD2 will force the SWR and
BSEL bits (FCF[1:0]) = 00. This causes the bootblock to be mapped into the lower
8 kB of code memory and the device will execute the ISP code in the boot block and
attempt to autobaud to the host. If the autobaud is successful the device will remain in
ISP mode. If, after approximately 400 ms, the autobaud is unsuccessful the boot
block code will check to see if the SoftICE flag is set (from a previous programming
operation). If the SoftICE flag is set the device will enter SoftICE mode. If the SoftICE
flag is cleared, the bootcode will execute a software reset causing the device to
execute the user code from block 0 starting at address 0000h. Note that an external
reset applied to the RST pin has the same effect as a power-on reset.
A software reset is executed by changing the SWR bit (FCF.1) from ‘0’ to ‘1’. A
software reset will reset the program counter to address 0000H and force both the
SWR and BSEL bits (FCF[1:0]) =10. This will result in the lower 8 kB of the user code
memory being mapped into the user code memory space. Thus the user's code will
be executed starting at address 0000h. A software reset will not change WDTC.2 or
RAM data. Other SFRs will be set to their reset values.
The device includes a brown-out detection circuit to protect the system from severe
supply voltage fluctuations. The P89LV51RD2's brown-out detection threshold is
2.35 V. When V
Fig 5. Power-on reset circuit.
DD
Rev. 03 — 11 October 2004
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drops below this voltage threshold, the brown-out detect triggers
8.2 k
10
m
W
F
C 2
C 1
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and RST to avoid programming at an
XTAL2
XTAL1
RST
8-bit microcontrollers with 80C51 core
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
V DD
P89LV51RD2
002aaa543
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