HT86B05 datasheet(52/79 Pages) HOLTEK

52 / 79 page

HT86BXX/HT86BRXX

Rev. 1.60

October 20, 2009

External RC Oscillation Converter

An external RC oscillation converter is implemented in

certain devices and is a function which allows analog

switch functions to be implemented. When used in con-

junction with the Analog Switch function up to eight

C/R-F can be implemented.

External RC Oscillation Converter Operation

The RC oscillation converter is composed of two 16-bit

count-up programmable timers. One is Timer 2, de-

scribed in the Timer section and the other is an addi-

tional counter known as Timer 4. The RC oscillation

converter is enabled when the RCO bit, which is bit 1 of

the RCOCR register, is set high. The RC oscillation con-

verter will then be composed of four registers, TMR2L,

TMR2H, TMR4L and TMR4H. The Timer 2 clock source

comes from the system clock or from the system

clock/4, the choice of which is determined by bits in the

RCOCCR register. The RC oscillation converter Timer 4

clock source comes from an external RC oscillator. As

the oscillation frequency is dependent upon external ca-

pacitance and resistance values, it can therefore be

used to detect the increased capacitance of a analog

switch pad.

There are six registers related to the RC oscillation con-

verter. These are, TMR2H, TMR2L, RCOCCR, TMR4H,

TMR4L and RCOCR. The internal timer clock is the in-

put clock source for TMR2H and TMR2L, while the ex-

ternal RC oscillator is the clock source input to TMR4H

and TMR4L. The OVB bit, which is bit 0 of the RCOCR

from either the Timer 2 overflows or Timer 4 overflow.

When a timer overflow occurs, the T2F bit is set and an

external RC oscillation converter interrupt occurs. When

the RC oscillation converter Timer 2 or Timer 4 over-

flows, the RCOCON bit is automatically reset to zero

and stops counting.

The resistor and capacitor form an oscillation circuit and

input to TMR4H and TMR4L. The RCOM0, RCOM1 and

RCOM2 bits of RCOCCR define the clock source of

Timer 2.

When the RCOCON bit, which is bit 4 of the RCOCCR

ing until Timer 2 or Timer 4 overflows. Now the timer

counter will generate an interrupt request flag which is

bit T2F, bit 4 of the INTCH register. Both Timer 2 and

Timer 4 will then stop counting and the RCOCON bit will

automatically be reset to "0" at the same time. Note that

if the RCOCON bit is high, the TMR2H, TMR2L, TMR4H

and TMR4L registers cannot be read or written to.

R C O C C R R e g i s t e r

b 7

b 0

U n d e f i n e d , r e a d a s z e r o

R C O M 2 R C O M 1 R C O M 0 R C O C O N

R C O s c i l l a t o r C o n v e r t e r E n a b l e

1 : E n a b l e

0 : D i s a b l e

T i m e r 2 C l o c k S o u r c e S e l e c t

R C O M 2

R C O M 1

R C O M 0

f S Y S

f S Y S / 4

U n d e f i n e d

RCOCCR Register

R C O C R R e g i s t e r

I n t e r r u p t S o u r c e S e l e c t

1 : T i m e r 4 o v e r f l o w

0 : T i m e r 2 o v e r f l o w

R C C o n v e r t e r M o d e

1 : E n a b l e

0 : D i s a b l e

b 7

b 0

U n d e f i n e d , r e a d a s z e r o

R C O

O V B

RCOCR Register

HT86B05 数据表(PDF) 52 Page - Holtek Semiconductor Inc

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