Hello,

I have a problem using a 4-mux-lcd with 24 segments / 4 coms together
with a MSP430F413. Almost anything works fine: my display shows all
segments as expected, scope shows voltages as shown in the datasheet
4-mux-example.

But if I want to trigger 4 certain segments whose lcd memory bits are
located at address 0x91 (the 4 lowest bits), all other segments become
lower intensity. I can measure that the voltage on all pins reduces by 1V.

For tests I have disconnected the lcd from my original TI-evaluation
board (no other external circuits) with same results. Further I have
disconnected the resistor ladder generating the lcd voltage-levels. So
there are only 0V and 3V. Therefore a voltage of 1V or 2V can't be
generated on no segment pin.
So I am astonished that I get a level of 2V at all segments anyway, if
I set one of the four lowest bits at address 0x91.

Is this a bug of the MSP or what goes on? I have tried 3 different MCUs.

Thanks for help!
Andreas

I recently had a similar problem.  It turned out that the LCD was wired 
incorrectly - one of the segment outputs drove one of the commons.  
Whenever I enabled that segment it would short to the common and drag 
down all the voltages.

I would find out exactly which segment pins are causing the problem and 
trace them.  Make sure that the LCD matches exactly the LCD in the 
schematic and test everything with a multimeter.

Good luck!  It can be a real pain to track down these problems sometimes...

-Adam

ab74de2000 wrote:

>Hello,
>
>I have a problem using a 4-mux-lcd with 24 segments / 4 coms together
>with a MSP430F413. Almost anything works fine: my display shows all
>segments as expected, scope shows voltages as shown in the datasheet
>4-mux-example.
>
>But if I want to trigger 4 certain segments whose lcd memory bits are
>located at address 0x91 (the 4 lowest bits), all other segments become
>lower intensity. I can measure that the voltage on all pins reduces by 1V.
>
>For tests I have disconnected the lcd from my original TI-evaluation
>board (no other external circuits) with same results. Further I have
>disconnected the resistor ladder generating the lcd voltage-levels. So
>there are only 0V and 3V. Therefore a voltage of 1V or 2V can't be
>generated on no segment pin.
>So I am astonished that I get a level of 2V at all segments anyway, if
>I set one of the four lowest bits at address 0x91.
>
>Is this a bug of the MSP or what goes on? I have tried 3 different MCUs.
>
>Thanks for help!
>Andreas
>
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