P89LPC954 datasheet(33/69 Pages) NXP

33 / 69 page

P89LPC952_954_4

Product data sheet

Rev. 04 — 24 July 2008

33 of 69

NXP Semiconductors

P89LPC952/954

8-bit microcontroller with 10-bit ADC

7.16.1 Reset vector

Following reset, the P89LPC952/954 will fetch instructions from either address 0000H or

the Boot address. The Boot address is formed by using the boot vector as the high byte of

the address and the low byte of the address = 00H.

The Boot address will be used if a UART break reset occurs, or the non-volatile Boot

Status bit (BOOTSTAT.0) = 1, or the device is forced into ISP mode during power-on (see

P89LPC952/954

User’s Manual). Otherwise, instructions will be fetched from address

0000H.

7.17 Timers/counters 0 and 1

The P89LPC952/954 has two general purpose counter/timers which are upward

compatible with the standard 80C51 Timer 0 and Timer 1. Both can be conﬁgured to

operate either as timers or event counters. An option to automatically toggle the T0 and/or

T1 pins upon timer overﬂow has been added.

In the ‘Timer’ function, the register is incremented every machine cycle.

In the ‘Counter’ function, the register is incremented in response to a 1-to-0 transition at its

corresponding external input pin, T0 or T1. In this function, the external input is sampled

once during every machine cycle.

Timer 0 and Timer 1 have ﬁve operating modes (Modes 0, 1, 2, 3 and 6). Modes 0, 1, 2

and 6 are the same for both Timers/Counters. Mode 3 is different.

7.17.1 Mode 0

Putting either Timer into Mode 0 makes it look like an 8048 Timer, which is an 8-bit

Counter with a divide-by-32 prescaler. In this mode, the Timer register is conﬁgured as a

13-bit register. Mode 0 operation is the same for Timer 0 and Timer 1.

7.17.2 Mode 1

Mode 1 is the same as Mode 0, except that all 16 bits of the timer register are used.

7.17.3 Mode 2

Mode 2 conﬁgures the Timer register as an 8-bit Counter with automatic reload. Mode 2

operation is the same for Timer 0 and Timer 1.

7.17.4 Mode 3

When Timer 1 is in Mode 3 it is stopped. Timer 0 in Mode 3 forms two separate 8-bit

counters and is provided for applications that require an extra 8-bit timer. When Timer 1 is

in Mode 3 it can still be used by the serial port as a baud rate generator.

7.17.5 Mode 6

In this mode, the corresponding timer can be changed to a PWM with a full period of

256 timer clocks.

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