80C32EBAA datasheet(10/62 Pages) PHILIPS

10 / 62 page

Philips Semiconductors

Product specification

80C32/87C52

CMOS single-chip 8-bit microcontrollers

1996 Aug 16

OSC

÷ 2

C/T2 = 0

C/T2 = 1

TR2

Control

TL2

(8-bits)

TH2

(8-bits)

÷ 16

RCAP2L

RCAP2H

EXEN2

Control

EXF2

Timer 2

Interrupt

T2EX Pin

Transition

Detector

T2 Pin

Reload

NOTE: OSC. Freq. is divided by 2, not 12.

÷ 2

“0”

“1”

RX Clock

÷ 16

TX Clock

“0”

“1”

“0”

“1”

Timer 1

Overflow

Note availability of additional external interrupt.

SMOD

RCLK

TCLK

SU00068

Figure 4. Timer 2 in Baud Rate Generator Mode

Table 2.

Timer 2 Operating Modes

RCLK + TCLK

CP/RL2

TR2

MODE

16-bit Auto-reload

16-bit Capture

Baud rate generator

(off)

Timer 2 as a baud rate generator is shown in Figure 4. This figure is

valid only if RCLK + TCLK = 1 in T2CON. Note that a rollover in TH2

does not set TF2, and will not generate an interrupt. Therefore, the

Timer 2 interrupt does not have to be disabled when Timer 2 is in

the baud rate generator mode. Note too, that if EXEN2 is set, a

1-to-0 transition in T2EX will set EXF2 but will not cause a reload

from (RCAP2H, RCAP2L) to (TH2, TL2). Thus when Timer 2 is in

use as a baud rate generator, T2EX can be used as an extra

external interrupt, if desired.

It should be noted that when Timer 2 is running (TR2 = 1) in “timer”

function in the baud rate generator mode, one should not try to read

or write TH2 or TL2. Under these conditions the timer is being

incremented every state time, and the results of a read or write may

not be accurate. The RCAP registers may be read, but should not

be written to, because a write might overlap a reload and cause

write and/or reload errors. Turn the timer off (clear TR2) before

accessing the Timer 2 or RCAP registers, in this case.

Timer/Counter 2 Set-up

Except for the baud rate generator mode, the values given for

T2CON do not include the setting of the TR2 bit. Therefore, bit TR2

must be set, separately, to turn the timer on. See Table 3 for set-up

of timer 2 as a timer. See Table 4 for set-up of timer 2 as a counter.

Using Timer/Counter 2 to Generate Baud Rates

For this purpose, Timer 2 must be used in the baud rate generating

mode. If Timer 2 is being clocked through pin T2 (P1.0) the baud

rate is:

Baud Rate

+ Timer 2 Overflow Rate

And if it is being clocked internally, the baud rate is:

Baud Rate

Oscillator Frequency

[65536

* (RCAP2H, RCAP2L)]

To obtain the reload value for RCAP2H and RCA02L, the above

equation can be rewritten as:

RCAP2H, RCAP2L

+ 65536 *

Oscillator Frequency

Baud Rate

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