HT82B40A datasheet(19/54 Pages) HOLTEK

19 / 54 page

HT82B40R/HT82B40A

Rev. 1.70

November 5, 2014

the port control register configures the pin as an input. It

should be noted that in the event counting mode, even if

the microcontroller is in the Power Down Mode, the

Timer/Event Counter will continue to record externally

changing logic events on the timer input pin. As a result

when the timer overflows it will generate a timer interrupt

and corresponding wake-up source.

Configuring the Pulse Width Measurement Mode

In this mode, the Timer/Event Counter can be utilised to

measure the width of external pulses applied to the ex-

ternal timer pin. To operate in this mode, the Operating

Mode Select bit pair, T0M1/T0M0 or T1M1/T1M0, in the

Timer Control Register must be set to the correct

valueas shown.

Control Register Operating Mode Select

Bits for the Pulse Width Measurement Mode

Bit7 Bit6

In this mode the internal clock, fSYS/4 is used as the in-

ternal clock for the Timer/Event Counters. After the

other bits in the Timer Control Register have been

setup, the enable bit T0ON or T1ON, which is bit 4 of the

Timer Control Register, can be set high to enable the

Timer/Event Counter, however it will not actually start

counting until an active edge is received on the external

timer pin.

If the Active Edge Select bit T0E or T1E, which is bit 3 of

the Timer Control Register, is low, once a high to low

transition has been received on the external timer pin,

TMR0 or TMR1, the Timer/Event Counter will start

counting until the external timer pin returns to its original

high level. At this point the enable bit will be automati-

cally reset to zero and the Timer/Event Counter will stop

counting. If the Active Edge Select bit is high, the

Timer/Event Counter will begin counting once a low to

high transition has been received on the external timer

pin and stop counting when the external timer pin re-

turns to its original low level. As before, the enable bit

will be automatically reset to zero and the Timer/Event

Counter will stop counting. It is important to note that in

the Pulse Width Measurement Mode, the enable bit is

automatically reset to zero when the external control

signal on the external timer pin returns to its original

level, whereas in the other two modes the enable bit can

only be reset to zero under program control.

The residual value in the Timer/Event Counter, which

can now be read by the program, therefore represents

the length of the pulse received on the external timer

pin. As the enable bit has now been reset, any further

transitions on the external timer pin will be ignored. Not

until the enable bit is again set high by the program can

the timer begin further pulse width measurements. In

this way, single shot pulse measurements can be easily

made.

It should be noted that in this mode the Timer/Event

Counter is controlled by logical transitions on the exter-

nal timer pin and not by the logic level. When the

Timer/Event Counter is full and overflows, an interrupt

signal is generated and the Timer/Event Counter will re-

load the value already loaded into the preload register

and continue counting. The interrupt can be disabled by

ensuring that the Timer/Event Counter Interrupt Enable

bit in the Interrupt Control Register, INTC, is reset to

zero.

As the external timer pin is shared with an I/O pin, to en-

sure that the pin is configured to operate as a pulse

width measurement pin, two things have to happen. The

first is to ensure that the Operating Mode Select bits in

the Timer Control Register place the Timer/Event Coun-

ter in the Pulse Width Measurement Mode, the second

is to ensure that the port control register configures the

pin as an input.ot by the logic level.

+ 1

+ 2

+ 3

+ 4

T i m e r

E x t e r n a l T i m e r

P i n I n p u t

T 0 O N o r T 1 O N

( w i t h T 0 E o r T 1 E = 0 )

P r e s c a l e r O u t p u t

I n c r e m e n t

T i m e r C o u n t e r

P r e s c a l e r O u t p u t i s s a m p l e d a t e v e r y f a l l i n g e d g e o f T 1 .

Pulse Width Measure Mode Timing Chart

HT82B40A 数据表(PDF) 19 Page - Holtek Semiconductor Inc

HT82B40A 数据表(HTML) 19 Page - Holtek Semiconductor Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

数据表下载