BD VFDs Application Note APN140

4. CONTROL PROCEDURE

4.4 Blanking

The driver of the BD VFD has a display blanking function. By using this blanking control, the output of driver can be turned on and off. This blanking function gives easy control of the display on/ off state, blinking and intensity of the display brightness.

"BK" = "High" (or "Open") Display OFF (Driver output OFF)

"BK" = "Low" Display ON (Driver output ON)

Refer to the following notice to avoid data error when controlling blanking data.

Do not change BK while data writing. (c.f. Fig 18a)
Do not change BK while CLK is L. (c.f. Fig 18a)
Do not change CLK L to H while LAT is H and BK is L.

Fig.18a Blanking Control Timing

4.4.1 Inter-Digit Blanking (For Multiplex Drive Only)

For a multiplex drive, the inter-digit blanking has to be maintained during data latching to avoid "ghost-illuminations" from the driver's switching characteristics. Refer to Figure 16c, 17b or 17d for the timing of the inter-digit blanking.

4.4.2 Brightness Control

The brightness level (intensity) can be adjusted by the blanking function.
In case of Grid/Anode independent type, use GBK or BKG (Blanking for Grid Driver) for the brightness controls instead of BK or BK1/2 (Blanking for Anode Driver).

4.4.2.1 Brightness Control in Static Drive

When the brightness is adjusted by the blanking function in a static driven VFD, the pulse of the signal needs to have a frequency of at least 90Hz in order to avoid a flickering display. Figure 18b shows the brightness change when adjustment is made by the blanking function in a static drive.

Brightness = (T-t_BK) / T x 100 (%) (Case of no blanking is 100%)

Fig.18b Brightness Control by Blanking

4.4.2.2 Brightness Control in Multiplex Drive

For the multiplex drive, the brightness control is attained by adjusting the blanking time (t_BK) in Figure 16 and 17. The relationships between the blanking timing and the brightness are the same as those of the static drive in Figure 18b.

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APN140