FAQ for F²MC-16LX Family

LCDC

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1. How do I control the brightness of the LCD controller? (Target: MB90800, MB90520)
2. How large capacitance do you recommend as the capacitor used to boost the LCD controller?
3. When I change the value of RAM for display during LCD display, the SEG waveform is not synchronized with the COM waveform. Why?
4. How much is the deviation of the dividing resistors built into the microcomputer?
5. As a noise measure, I installed capacitors in the SEG and COM pins. However, as a result of the installation, a different reference voltage is output and waveforms become dull. Why?
6. As a result of installing capacitors in the SEG and COM pins as a noise measure, output waveforms like beard whisker. Why?
7. If a transition is made to the STOP mode during LCDC operation, the LCDC display appears for an instant. (Target: MB90420G/ 425G)
8. Can I input Vcc voltage or higher to the V3 pin?
9. LCD is turned on according to settings of 1/2 bias and 1/2 duty but why does LCD display become dim?

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How do I control the brightness of the LCD controller? (Target: MB90800, MB90520)

• Answer :
  You can adjust the brightness of the LCD controller by adjusting the resistance between the Vcc and V3 pins.

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How large capacitance do you recommend as the capacitor used to boost the LCD controller?

• Answer :
  See an appropriate hardware manual.

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When I change the value of RAM for display during LCD display, the SEG waveform is not synchronized with the COM waveform. Why?

• Answer :
  When RAM for display is rewritten, the SEG signal is not synchronized with the COM signal because SEG display is immediately changed. When RAM for display remains unchanged, the SEG waveform is synchronized with the COM waveform.

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How much is the deviation of the dividing resistors built into the microcomputer?

• Answer :
  LCD dividing resistors do not vary individually but shift wholly. This does not mean that one of the three dividing resistors built into the microcomputer becomes 50 kΩ and the two others become 200 kΩ. The three dividing resistors vary between 50 kΩ and 200 kΩ.

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As a noise measure, I installed capacitors in the SEG and COM pins. However, as a result of the installation, a different reference voltage is output and waveforms become dull. Why?

• Answer :
  When capacitors are installed in the SEG and COM pins, current flows to cause capacitors to be charged or discharged. For this reason, each reference voltage differs or waveforms become dull.

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As a result of installing capacitors in the SEG and COM pins as a noise measure, output waveforms like beard whisker. Why?

• Answer :
  When the output voltage is switched, waveforms like whisker appear because the SEG and COM pins are instantaneously connected to either of the reference voltages. You can narrow this whisker waveform by connecting capacitors to the V0 to V3 pins.

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If a transition is made to the STOP mode during LCDC operation, the LCDC display appears for an instant. (Target: MB90420G/ 425G)

• Answer :
  We think that, when a transition is made to the STOP mode, the BK bit of the LCDC control register (LCRL) is set to "0." Set BK to "1" (No display) and then confirm the operation.

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Can I input Vcc voltage or higher to the V3 pin?

• Answer :
  Input Vcc voltage or lower to the V3 pin. (This is to be written in the data sheet.)

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LCD is turned on according to settings of 1/2 bias and 1/2 duty but why does LCD display become dim?

• Answer :
  When 1/2 bias and 1/2 duty are used, the DTHC bit (bit 12) of the LCRH register SHOULD be set to "1". Currently, this is not written in the manual but we requested to correct the incorrect description, so it is to be written in the error table.