SC668 datasheet(40/46 Pages) SEMTECH

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SC668

ADC Function Register (12h)

This register is used to enable the functions of the ADC

and store related status bits. The ADC converts the analog

output voltage signal of an ALS (Ambient Light Sense)

circuit and stores the digital conversion in the ADC output

OUT (register 13h). The data may be used to automati-

cally adjust the brightness of bank #1 backlights in

response to changes in ambient lighting conditions.

AD_CMP [D7]

This bit indicates the comparison of AD

OUT (register 13h) to

both AD

RISE (register 14h) and ADFALL(register 15h). When

OUT exceeds ADRISE, AD_CMP = 1. When ADOUT falls below

FALL , AD_CMP = 0.

AD_INT [D6]

This bit is set when the AD_CMP bit [D7] changes state. If

the AD_SATEN [D5] bit is set, AD_INT bit [D6] may also be

used to indicate an overflow or underflow in AD

OUT (register

13h). This bit is cleared when ADC function register (12h) is

read, or when writing INT_CLR bit [D2] equal to one.

The AD_INT bit provides a flag indicating that the ADI

input has exceeded a threshold level, or indicates that an

overflow or underflow condition exists. Figure 28 shows

the AD_INT flag interrupt states.

Bit

AD_CMP

changes

state

Interrupt is set

AD_INT ⇒ 1

Interrupt is reset

AD_INT ⇒ 0

Read

Write

CLR_INT = 1

AD_SAT = 0

AD_OF = 1

AD_UF = 1

and

AD_SAT

0 ⇒ 1

AD_SAT = 1

and

AD_OF

0 ⇒ 1

AD_UF

0 ⇒ 1

Figure 28 — ADC Interrupt State Diagram

AD_SATEN [D5]

This bit, when set, allows an underflow or overflow to gen-

erate an interrupt which sets the AD_INT bit [D6]. When

AD_SATEN = 1, an overflow or underflow condition in reg-

ister 13h will set the AD_INT bit.

AD_OF [D4]

This bit indicates an overflow condition in register 13h. This

bit is set to one whenever AD

OUT becomes ADOUT > F8h.

AD_UF [D3]

This bit indicates an underflow condition in register 13h.This

bit is set to one whenever AD

OUT becomes ADOUT < 08h.

INT_CLR [D2]

Writing a one to this bit automatically resets bit AD_INT to

zero. INT_CLR resets itself and will always read as zero.

AD_AUTO [D1]

When the AD_AUTO bit is high, the contents of the AD

OUT,

RISE, and ADFALL registers are compared and used to control

the brightness of backlight bank #1. AD

OUT is compared with

two threshold values contained in registers AD

RISE and

FALL. If ADOUT becomes greater than ADRISE, bank #1 will

change to the bank #1 target backlight setting of register

06h. If AD

OUT becomes less than ADFALL, bank #1 will change

to the bank #1 backlight setting from register 02h.

When the AD_AUTO bit is low, the comparison of AD

OUT to

RISE and ADFALL is disabled so that bank #1 does not react

to changes in the value of AD

OUT, ADRISE, or ADFALL.

AD_EN [D0]

When the AD_EN bit is high, the ADC is activated and the

results of each conversion are stored in AD

OUT (register 13h).

The functions of the AD_AUTO and AD_EN bits are shown

in Table 22.

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