BH1721FVC

Technical Note

5/15

www.rohm.com

2011.11 - Rev.B

© 2011 ROHM Co., Ltd. All rights reserved.

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Instruction Set Architecture

Instruction

Opecode

Comments

Power Down

0000_0000

No active state.

Power On

0000_0001

Waiting for measurement command.

Continuously Auto-Resolution Mode

0001_0000

0010_0000

Switch measurement mode automatically by illuminance.

Continuously H-Resolution Mode

0001_0010

0010_0010

Start measurement at 1lx resolution.

Measurement Time is typically 120ms.

Continuously L-Resolution Mode

0001_0011

0001_0110

0010_0011

0010_0110

Start measurement at 8lx resolution.

Measurement Time is typically 16ms.

Change Measurement time

( High bit )

010_MT[9,8,7,6,5]

Change measurement time.

※

Please refer "adjust measurement result for influence of optical window."

Change Masurement time

( Low bit )

011_MT[4]_XXXX

Change measurement time.

※

Please refer "adjust measurement result for influence of optical window."

※

Don't input the other opecode.

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Measurement mode explanation

Measurement Mode

Measurement Time.

Measurement Range.

Resolution

H-Resolution Mode

Typ. 120ms

0 - 8191 lx

1 lx

L-Resolution Mode

Typ. 16ms

0 - 65528 lx

8 lx

We recommend to use H-Resolution Mode.

Measurement time (integration time) of H-Resolution Mode is so long that some kind of noise (including in 50Hz / 60Hz

noise) is rejected. And H-Resolution Mode is 1 lx resolution so that it is suitable for darkness (less than 20 lx)

Auto-Resolution mode selects measurement mode automatically. It is determined after 16ms (typ.) passes from

measurement start. If BH1721FVC judges that current illuminance is more than 4000 lx, then Data is output at L-resolution

mode, else Data is output after 120ms(typ.) from measurement start at H-resolution mode. Please refer below flow chart.

Lux > 4000

Start

Select mode

Lux <= 4000

DATA output at L-resolution mode

after 16ms.(typ.)

Data output at H-resolution mode after

120ms passes from measurement start.

Auto-Resolution mode measurement