P87LPC764FN datasheet(28/60 Pages) PHILIPS

28 / 60 page

Philips Semiconductors

Product data

P87LPC764

Low power, low price, low pin count (20 pin)

microcontroller with 4 kbyte OTP

2003 Sep 03

Low Voltage EPROM Operation

The EPROM array contains some analog circuits that are not

required when VDD is less than 4 V, but are required for a VDD

greater than 4 V. The LPEP bit (AUXR.4), when set by software, will

power down these analog circuits resulting in a reduced supply

current. LPEP is cleared only by power-on reset, so it may be set

ONLY for applications that always operate with VDD less than 4 V.

Reset

The P87LPC764 has an integrated power-on reset circuit which

always provides a reset when power is initially applied to the device.

It is recommended to use the internal reset whenever possible to

save external components and to be able to use pin P1.5 as a

general-purpose input pin.

The P87LPC764 can additionally be configured to use P1.5 as an

external active-low reset pin RST by programming the RPD bit in the

User Configuration Register UCFG1 to 0. The internal reset is still

active on power-up of the device. While the signal on the RST pin is

low, the P87LPC764 is held in reset until the signal goes high.

The watchdog timer on the LPC764 can act as an oscillator fail

detect because it uses an independent, fully on-chip oscillator.

UCFG1 is described in the System Configuration Bytes section of

this datasheet.

SU01169

87LPC764

P1.5

Pin is used as

digital input pin

Internal power-on

Reset active

UCFG1.RPD = 1 (default)

87LPC764

RST

Pin is used as

active-low reset pin

Internal power-on

Reset active

UCFG1.RPD = 0

Figure 20. Using pin P1.5 as general purpose input pin or as low-active reset pin

SU01170

CHIP RESET

CPU

CLOCK

RESET

TIMING

RPD (UCFG1.6)

WDT

MODULE

SOFTWARE RESET

SRST (AUXR1.3)

POWER MONITOR

RESET

RST/VPP PIN

WDTE (UCFG1.7)

Figure 21. Block Diagram Showing Reset Sources

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