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SNAD01B

8-CHANNEL 8-BIT ADC

Program 5: Battery Low Detection

SNC520

SNAD01B

START

CLK

DIO

VDD

AVDD

REF

VSS

AVSS

CH[7]

VDD

0.1uF

VDD

VSS

P20

P21

P22

VDD

Battery:

1.5Vx3

An application uses three 1.5V batteries for power supply. During operation, the

power of batteries keeps consumed and the voltage of battery keeps going down.

Now, voltage lower than 3.6V is treated as “Battery Low”. The ADC and bandgap

reference circuit in SNAD01B can be utilized to detect “Battery Low”.

The voltage through channel 7 to ADC is reduced to 1/6*VDD (Figure10). Thus, when

VDD=3.6V, the voltage into ADC is around 0.6V. And bandgap is chosen for

reference voltage (approximately 1.17V within the whole operation voltage range).

The value acquired from ADC is about (0.6/1.17)*256=131. For simplification

consideration, we choose “ADC’s readout < 128” as “Battery Low” condition.

;; Inherit from program 1

;; Enter Power-down Mode (0)

CheckBattery:

@Set_Control_Reg

#0, #1, #1, #0

;; Set rf=1, turn-on bandgap

@Set_Attrib

#1, #1, #1, #0, #0, #0, #1, #1 ;; Switch Ch7 to Analog

mov

m15

CheckAgain:

@Read_ADC #1, #1, #1

;; Read Ch7

mov

#1000b

and

ad_out_h

caje

#1000b Battery_Low_No

;; if (Value>=128) then Not Battery Low

mov

m15

inca

mov

m15

caje

Battery_Low_Yes

;; if (Value<128) for 3 times, then

jmp

CheckAgain

;; battery low.

Battery_Low_Yes:

mov

m14

Version: 1.3

July 31, 2003

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