HT66F016 datasheet(82/116 Pages) HOLTEK

82 / 116 page

HT66F016/HT66F017/HT68F016/HT68F017

Rev. 1.00

May 14, 2012

Comparators

An analog comparator is contained within these de-

vices. These functions offer flexibility via their register

controlled features such as power-down, polarity select,

hysteresis etc. In sharing their pins with normal I/O pins

the comparators do not waste precious I/O pins if there

functions are otherwise unused.

Comparator Operation

The device contains a comparator function which is

used to compare two analog voltages and provide an

output based on their difference. Full control over the in-

ternal comparators is provided via the control register

CPC assigned to the comparator. The comparator out-

put is recorded via a bit in the control register, but can

also be transferred out onto a shared I/O pin. Additional

comparator functions include, output polarity, hysteresis

functions and power down control.

Any pull-high resistors connected to the shared com-

parator input pins will be automatically disconnected

when the comparator is enabled. As the comparator in-

puts approach their switching level, some spurious out-

put signals may be generated on the comparator output

due to the slow rising or falling nature of the input sig-

nals. This can be minimised by selecting the hysteresis

function will apply a small amount of positive feedback

to the comparator. Ideally the comparator should switch

at the point where the positive and negative inputs sig-

nals are at the same voltage level, however, unavoid-

able input offsets introduce some uncertainties here.

The hysteresis function, if enabled, also increases the

switching offset value.

Comparator Interrupt

The comparator possesses its own interrupt function.

When the comparator output changes state, its relevant

interrupt flag will be set, and if the corresponding inter-

rupt enable bit is set, then a jump to its relevant interrupt

vector will be executed. Note that it is the changing state

of the COUT bit and not the output pin which generates

an interrupt. If the microcontroller is in the SLEEP or

IDLE Mode and the Comparator is enabled, then if the

external input lines cause the Comparator output to

change state, the resulting generated interrupt flag will

also generate a wake-up. If it is required to disable a

wake-up from occurring, then the interrupt flag should

be first set high before entering the SLEEP or IDLE

Mode.

Programming Considerations

If the comparator is enabled, it will remain active when

the microcontroller enters the SLEEP or IDLE Mode,

however as it will consume a certain amount of power,

the user may wish to consider disabling it before the

SLEEP or IDLE Mode is entered.

As comparator pins are shared with normal I/O pins the

I/O registers for these pins will be read as zero (port con-

trol register is

²1²) or read as port data register value

(port control register is

²0²) if the comparator function is

enabled.

C +

C -

C P O L

C O U T

C X

C S E L

Comparator

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