HT45R37V datasheet(32/90 Pages) HOLTEK

32 / 90 page

HT45R37V

Rev. 1.00

October 20, 2009

The values in Timer A and Timer B is changed by writing

to the high byte registers, TMRAH and TMRBH, but writ-

ing to the low byte registers TMRAL and TMRBL will

keep the values in Timer A and Timer B unchanged.

Reading registers TMRAH and TMRBH will also latch

the TMRAL TMRBL values into the low byte buffer to

avoid false timing problems. Reading from registers

TMRAL and TMRBL returns the contents of the low byte

buffer only. Therefore, the low byte of Timer A and Timer

B cannot be read directly. TMRAH and TMRBH must be

read first to ensure that the low byte contents of Timer A

and Timer B are latched into the buffer.

The external resistor and capacitor, together with inter-

nal inverters, form an oscillation circuit which is the clock

source for Timer B and therefore the input to registers

TMRBL and TMRBH. The RCOM0, RCOM1 and

RCOM2 bits of RCOCCR define the clock source of

Timer A.

If the RCOCON bit in the RCOCCR register is set high,

Timer A and Timer B will start counting until either Timer

A or Timer B overflows. The relevant Timer will then gen-

erate an interrupt request flag which is the RCOCF bit in

the INTC1 register. Timer A and Timer B will stop count-

ing and will also reset the RCOCON bit to zero at the

same time. If the RCOCON bit is set high, then the

TMRAL/TMRAH and TMRBL/TMRBH register cannot

be read or written to.

C/R to F Converter Analog Switches

The device contains only one internal C/R to F converter

function, however it can be connected to any of the 9 ex-

ternal channels using its internal analog switch function.

This enables applications such as multi-channel or ma-

trix touch switch applications to be implemented. The

bits in the ASCR0~ASCR1 registers select which of the

9-channels is to be connected to the internal C/R to F

converter. The bits in the ASCR2 register selects what

happens to the channel when the channel is inactive.

When a channel is inactive it can be selected to be

pulled low to ground or not using bits in the ASCR2 reg-

ister. As there are only 8-bits to control 9-channels the

function is selected in channel pairs. There are configu-

ration options which must first be selected to choose

which pins are to be used as inputs to the C/R to F con-

verter.

If the configuration options have selected PA0~PA7 to

be normal I/O pins, then the corresponding bit 0~bit7

bits in the ASCR0 register will have no function and will

be read as zero. Similarly if the configuration options

have selected PD0 to be normal I/O pins, then the corre-

sponding bit 0 bit in the ASCR1 register will have no

function and will be read as zero.

If the configuration options have selected PA0~PA7 to

be normal I/O pins, then the corresponding bits in the

ASCR2 register, bit 0 ~ bit3, must be cleared to zero to

disable the RC0/RC1, RC2/RC3, RC4/RC5 and RC6/RC7

pull-low resistors. Similarly if the configuration options

have selected PD0 to be normal I/O pin, then the corre-

sponding bits in the ASCR2 register, bit 4, must be cleared

to zero to disable the RC8 pull-low resistor. the ASCR2

tion program.

A . S . 0

A . S . 1

A . S . 7

A . S . 8

A S C R 0

A S C R 1

A S C R 2

R C 0

R C 1

R C 7

R C 8

R C O U T / I N

R R E F

T i m e r B

C l o c k S o u r c e

C R E F

A n a l o g

S w i t c h e s

R e g i s t e r s

R C 0 ~

R C 8

A . S . 0 ~ A . S . 8

R C 0 ~ R C 8

P u l l - l o w

A n a l o g S w i t c h

E x t e r n a l R C

M C U

A S C R 0 / A S C R 1

R e g i s t e r C o n t r o l

A S C R 2

R e g i s t e r C o n t r o l

Analog Switches and C/R to F Oscillator

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