P89V52X2FN datasheet(23/56 Pages) PHILIPS

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P89V52X2_1

Preliminary data sheet

Rev. 01 — 7 June 2007

23 of 56

NXP Semiconductors

P89V52X2

80C51 with 256 B RAM, 192 B data EEPROM

When a logic 0 is applied at pin T2EX this causes Timer 2 to count down. The timer will

underflow when TL2 and TH2 become equal to the value stored in RCAP2L and

RCAP2H. Timer 2 underflow sets the TF2 flag and causes 0FFFFH to be reloaded into the

timer registers TL2 and TH2. The external flag EXF2 toggles when Timer 2 underflows or

overflows. This EXF2 bit can be used as a 17th bit of resolution if needed.

6.9.3 Programmable clock-out

A 50 % duty cycle clock can be programmed to come out on pin T2 (P1.0). This pin,

besides being a regular I/O pin, has two additional functions. It can be programmed:

1. To input the external clock for Timer/Counter 2, or

2. To output a 50 % duty cycle clock ranging from 122 Hz to 8 MHz at a 16 MHz

operating frequency.

To configure the Timer/Counter 2 as a clock generator, bit C/T2 (in T2CON) must be

cleared and bit T2OE in T2MOD must be set. Bit TR2 (T2CON.2) also must be set to start

the timer.

The Clock-Out frequency depends on the oscillator frequency and the reload value of

Timer 2 capture registers (RCAP2H, RCAP2L) as shown in Equation 2:

(2)

Where (RCAP2H, RCAP2L) = the content of RCAP2H and RCAP2L taken as a 16-bit

unsigned integer.

In the Clock-Out mode Timer 2 rollovers will not generate an interrupt. This is similar to

when it is used as a baud rate generator.

6.9.4 Baud rate generator mode

Bits TCLK and/or RCLK in T2CON allow the UART transmit and receive baud rates to be

derived from either Timer 1 or Timer 2 (See Section 6.10 for details). When TCLK = 0,

Timer 1 is used as the UART transmit baud rate generator. When TCLK = 1, Timer 2 is

Fig 16. Timer 2 in Auto Reload mode (DCEN = 1)

002aaa525

TL2

(8-bits)

TH2

(8-bits)

TF2

EXF2

underflow

timer 2

interrupt

RCAP2L RCAP2H

FFH

overflow

(down-counting reload value)

(up-counting reload value)

count direction

1 = up

0 = down

T2EX pin

toggle

OSC

÷6

T2 pin

C/T2 = 0

C/T2 = 1

control

TR2

OscillatorFrequency

65536

RCAP2H RCAP2L

()

∠

()

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P89V52X2FN Datasheet(PDF) 23 Page - NXP Semiconductors

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