P83C524 datasheet(27/76 Pages) PHILIPS

27 / 76 page

1997 Dec 15

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers

P83C524; P80C528; P83C528

11.2.2

CAPTURE MODE

In the capture mode (see Fig.14) there are two options

which are selected by bit EXEN2 in T2CON. If EXEN2 = 0,

then Timer 2 is a 16-bit timer/counter which on overflow

sets bit TF2 (Timer 2 overflow bit). TF2 can be used to

generate an interrupt. If EXEN2 = 1, Timer 2 operates as

above, with the added feature that a HIGH-to-LOW

transition at the external input T2EX causes the current

value in Timer 2 registers (TL2 and TH2) to be captured

into registers RCAP2L and RCAP2H, respectively. The

HIGH-to-LOW transition of T2EX also causes bit EXF2 in

T2CON to be set. EXF2 can be used to generate an

interrupt.

11.2.3

AUTOMATIC RELOAD MODE

In the automatic reload mode (see Fig.15)there are two

options which are selected by bit EXEN2 in T2CON. If

EXEN2 = 0, then a Timer 2 overflow sets TF2 and causes

the Timer 2 registers to be reloaded with the 16-bit value

in registers RCAP2L and RCAP2H, which are preset by

software.

If EXEN2 = 1, Timer 2 operates as above, with the added

feature that a HIGH-to-LOW transition at the external input

T2EX triggers the 16-bit reload and sets EXF2.

11.2.4

BAUD RATE GENERATOR MODE

The baud rate generator mode (see Fig.16) is selected by

RCLK = 1 and/or TCLK = 1 in T2CON. Overflows of either

Timer 2 or Timer 1 can be used independently for

generating baud rates for transmit and receive. The baud

rate generation by Timer 1 and/or Timer 2 is used for the

Serial Port in Mode 1 and Mode 3. The baud rate

generation mode is similar to the automatic reload mode,

in that a rollover in TH2 causes the Timer 2 registers to be

reloaded with the 16-bit value in registers RCAP2L and

RCAP2H, which are preset by software. The baud rate for

the Serial Port in Modes 1 and 3 are determined by

Timer 2's overflow rate as follows:

Timer 2 can be configured for either 'timer' or 'counter'

operation. In timer operation a prescaler divides the

oscillator frequency by 2 (by 12 in the previous modes) and

the baud rate is given by the formula:

In this mode an overflow of Timer 2 does not set TF2. If

EXEN2 = 1, a HIGH-to-LOW transition at pin T2EX sets

EXF2 and can be used to generate an interrupt.

Baud Rate

Timer 2 overflow rate

--------------------------------------------------------

Baud Rate

oscillator frequency

65536

RCAP2H RCAP2L

)

]

–

[

-------------------------------------------------------------------------------------------------------

Fig.14 Timer 2 in capture mode.

handbook, full pagewidth

MBC468 - 1

TL2

(8 BITS)

TR2

control

TH2

(8 BITS)

RCAP2L

RCAP2H

EXF2

TF2

timer 2

interrupt

EXEN2

control

C/T2 = 1

T2 PIN

OSC

transition

detector

T2EX PIN

C/T2 = 0

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