P89V51RB2BBC datasheet(27/80 Pages) NXP

27 / 80 page

P89V51RB2_RC2_RD2_5

Product data sheet

Rev. 05 — 12 November 2009

27 of 80

NXP Semiconductors

P89V51RB2/RC2/RD2

8-bit microcontrollers with 80C51 core

6.4 Timers/counters 0 and 1

The two 16-bit Timer/counter registers: Timer 0 and Timer 1 can be conﬁgured to operate

either as timers or event counters (see Table 14 and Table 15).

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

think of it as counting machine cycles. Since a machine cycle consists of six oscillator

periods, the count rate is 1

⁄

6 of the oscillator frequency.

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 every machine cycle.

When the samples show a high in one cycle and a low in the next cycle, the count is

incremented. The new count value appears in the register in the machine cycle following

the one in which the transition was detected. Since it takes two machine cycles (12

oscillator periods) for 1-to-0 transition to be recognized, the maximum count rate is 1

⁄

12 of

the oscillator frequency. There are no restrictions on the duty cycle of the external input

signal, but to ensure that a given level is sampled at least once before it changes, it should

be held for at least one full machine cycle. In addition to the ‘Timer’ or ‘Counter’ selection,

Timer 0 and Timer 1 have four operating modes from which to select.

The ‘Timer’ or ‘Counter’ function is selected by control bits C/T in the Special Function

selected by bit-pairs (M1, M0) in TMOD. Modes 0, 1, and 2 are the same for both

Timers/counters. Mode 3 is different. The four operating modes are described in the

following text.

Program Security Bit, Double

Clock

Input parameters:

R1 = 05H

DPL = 01H = security bit

DPL = 05H = Double Clock

Return parameter(s):

ACC = 00 = pass

ACC=!00=fail

Read Security Bit, Double Clock,

SoftICE

Input parameters:

ACC = 07H

Return parameter(s):

ACC = 00 SoftICE S/N-match 0 SB 0 DBL_CLK

Erase sector

Input parameters:

R1 = 08H

DPH = sector address high byte

DPL = sector address low byte

Return parameter(s):

ACC = 00 = pass

ACC = !00 = fail

Table 13.

IAP function calls …continued

IAP function

IAP call parameters

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