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PSoC™ 4

FeZh_2719436
Level 1
Level 1

The Segment LCD can work properly when using High Speed Mode with hs_clk set to 1M ~ 3M Hz. But when set to use Low Speed Mode, the LCD can't work properly, with all the icons displayed on LCD. I can't turn off any icon by writing LCD_Seg_PIXEL_STATE_OFF to the corresponding pixel, while this method works OK in high speed mode. Currently using the PWM Driving Mode, but Digital Correlation has the same issue.  Could somebody kindly tell me how to drive Segment LCD in Low speed Mode?

I also notice that with High Speed mode, when the hs_clk is set to a low enough value (such as 100K), the same issue happens, i.e., all the icons are displayed and can't be turned off.

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PSa_795526
Level 4
First like given 10 replies posted 5 solutions authored
Level 4

Hi,

The PWM Driving mode of segment LCD requires external series resistors for the low speed ILO based operation, for filtering the PWM waveform (whereas for MHz frequencies the intrinsic resistance of the ITO traces and pin drive impedance is sufficient)

This is mentioned in page 33 of the PSoC4 SegLCD component datasheet https://www.cypress.com/file/220341/download

"In order to drive a low capacitance display with acceptable ripple and rise/fall time using a 32 kHz PWM an additional external series resistance of 100 k - 1 M ohm is required. External Resistors are not required for PWM frequencies of greater than ~1 MHz."

The Digital correlation method does not seem to require external resistors. However the contrast achieved in digital correlation mode is lesser than the PWM driving mode. Does the digital correlation mode look fine on your LCD with the MHz clock(1-3 MHz) ?

Best Regards,

Prem Sai

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