P89CV51RB2_09 datasheet(29/76 Pages) NXP

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P89CV51RB2_RC2_RD2_3

Product data sheet

Rev. 03 — 25 August 2009

29 of 76

NXP Semiconductors

P89CV51RB2/RC2/RD2

80C51 with 1 kB RAM, SPI

6.4.2 Mode 1

Mode 1 is the same as Mode 0, except that all 16 bits of the timer register (THn and TLn)

are used; see Figure 8.

6.4.3 Mode 2

Mode 2 conﬁgures the timer register as an 8-bit counter (TLn) with automatic reload, as

shown in Figure 9. Overﬂow from TLn not only sets TFn, but also reloads TLn with the

contents of THn, which must be preset by software. The reload leaves THn unchanged.

Mode 2 operation is the same for Timer 0 and Timer 1.

6.4.4 Mode 3

When Timer 1 is in Mode 3 it is stopped (holds its count). The effect is the same as setting

TR1=0.

Timer 0 in Mode 3 establishes TL0 and TH0 as two separate 8-bit counters. The logic for

Mode 3 and Timer 0 is shown in Figure 10. TL0 uses the Timer 0 control bits: T0C/T,

T0GATE, TR0, INT0, and TF0. TH0 is locked into a timer function (counting machine

cycles) and takes over the use of TR1 and TF1 from Timer 1. Thus, TH0 now controls the

Timer 1 interrupt.

Mode 3 is provided for applications that require an extra 8-bit timer. With Timer 0 in

mode 3, the P89CV51RB2/RC2/RD2 can look like it has an additional timer.

Note: When Timer 0 is in Mode 3, Timer 1 can be turned on and off by switching it into

and out of its own Mode 3. It can still be used by the serial port as a baud rate generator,

or in any application not requiring an interrupt.

Fig 8.

Timer/counter 0 or 1 in Mode 1 (16-bit counter)

002aaa520

osc/6

Tn pin

TRn

TnGate

INTn pin

C/T = 0

C/T = 1

TLn

(8-bits)

THn

(8-bits)

TFn

control

overflow

interrupt

Fig 9.

Timer/counter 0 or 1 in Mode 2 (8-bit auto-reload)

002aaa521

osc/6

Tn pin

TRn

TnGate

INTn pin

TLn

(8-bits)

THn

(8-bits)

TFn

control

overflow

reload

interrupt

C/T = 0

C/T = 1

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