Philips Semiconductors

User’s Manual - Preliminary -

 

 

RESET

P89LPC901/902/903

9. RESET

The P1.5/RST pin can function as either an active low reset input or as a digital input, P1.5. The RPE (Reset Pin Enable) bit in UCFG1, when set to 1, enables the external reset input function on P1.5. When cleared, P1.5 may be used as an input pin.

NOTE: During a power-on sequence, The RPE selection is overriden and this pin will always functions as a reset input. An external circuit connected to this pin should not hold this pin low during a Power-on sequence as this will keep the device in reset. After power-on this input will function either as an external reset input or as a digital input as defined by the RPE bit. Only a power- on reset will temporarily override the selection defined by RPE bit. Other sources of reset will not override the RPE bit.

NOTE: During a power cycle, VDD must fall below VPOR (see "DC electrical characteristics" in the datasheet) before pwoer is reapplied, in order to ensure a power-on reset.

Reset can be triggered from the following sources (see Figure 9-1):

•External reset pin (during power-on or if user configured via UCFG1);

•Power-on Detect;

•Brownout Detect;

•Watchdog Timer;

•Software reset;

•UART break-character detect reset. (P89LPC903)

For every reset source, there is a flag in the Reset Register, RSTSRC. The user can read this register to determine the most recent reset source. These flag bits can be cleared in software by writing a ’0’ to the corresponding bit. More than one flag bit may be set:

•During a power-on reset, both POF and BOF are set but the other flag bits are cleared.

•For any other reset, any previously set flag bits that have not been cleared will remain set.

Power-On reset code execution

The P89LPC901/902/903 contains two special Flash elements: the BOOT VECTOR and the Boot Status Bit. Following reset, the P89LPC901/902/903 examines the contents of the Boot Status Bit. If the Boot Status Bit is set to zero, power-up execution starts at location 0000H, which is the normal start address of the user’s application code. When the Boot Status Bit is set to a one, the contents of the Boot Vector is used as the high byte of the execution address and the low byte is set to 00H. The fac- tory default setting is 00H. A UART break-detect reset (P89LPC903) will have the same effect as a non-zero Status Bit.

RPE (UCFG1.6)

RST Pin

WDTE (UCFG1.7)

Watchdog Timer Reset

Software Reset SRST (AUXR1.3)

Power-on Detect

UART Break Detect

EBRR (AUXR1.6)

Brownout Detect Reset

BOPD (PCON.5)

Chip Reset

Figure 9-1: Block Diagram of Reset

2003 Dec 8

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Philips P89LPC903, P89LPC901, P89LPC902 user manual Power-On reset code execution, Block Diagram of Reset
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P89LPC903, P89LPC902, P89LPC901 specifications

The Philips P89LPC901, P89LPC902, and P89LPC903 are a series of 8-bit microcontrollers designed for embedded system applications. These models, which belong to the LPC900 series, are notable for their affordability and versatility, making them an attractive choice for both hobbyists and professional developers.

One of the core features of the P89LPC901, P89LPC902, and P89LPC903 microcontrollers is their powerful 8-bit architecture. Operating at clock speeds up to 20 MHz, they deliver efficient performance suited for a range of tasks. Each model includes a comprehensive instruction set that supports various data manipulation and arithmetic functions, enabling extensive programming capabilities.

These microcontrollers come with built-in memory, with configurations that vary among the three models. The P89LPC901 typically features 4 KB of Flash memory and 256 bytes of RAM, while the P89LPC902 and P89LPC903 offer enhanced memory options. This Flash memory allows for reprogrammability, making it easier to update and modify applications as needed.

Another significant characteristic of the LPC900 series is their integrated peripherals. These models are equipped with a variety of I/O ports, allowing for easy interfacing with other devices and components. The P89LPC901 supports up to 32 I/O pins, while the P89LPC902 and P89LPC903 provide additional features such as analog-to-digital converters (ADCs), timers, and serial communication interfaces. This broad range of peripherals empowers developers to design complex applications without needing extra hardware.

Power consumption is also a key consideration for microcontroller applications. The P89LPC901, P89LPC902, and P89LPC903 are designed with low power consumption in mind, making them ideal for battery-operated devices and energy-efficient projects. They can operate in various power modes, allowing for greater flexibility in deployment.

In terms of technology, these microcontrollers utilize advanced CMOS technology, ensuring high reliability and durability. Their design offers a robust solution for numerous applications, including consumer electronics, industrial controls, and automation systems.

In summary, the Philips P89LPC901, P89LPC902, and P89LPC903 microcontrollers present an attractive combination of performance, integrated peripherals, low power consumption, and versatility. Their features cater to a wide array of applications, keeping them relevant in a rapidly evolving technology landscape. For hobbyists and professionals alike, these microcontrollers represent a reliable foundation for embedded system development.
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