STM32L152V8 and LCD_CAPA and external decoupling

[crew]

Posted on December 21, 2015 at 17:37

I have an STM32L152V8 running a large LCD using 1/4 bias and 1/4 duty. It works, but needs a little capacitive decoupling on the bias rails. I am using eternal decoupling pins PA0, PA2 and PA12, have enable external access to the bias signals with 'SYSCFG->PMC |= x0000000E' (LCD_CAPA) and have verified with my debugger that the register is indeed loaded with that value. I have also enabled those 3 pins as inputs per the manual.

The pins PB0, PB2 & PB12 are just floating, they should be .825, 1.65 and 2.45v. Apparently the pins are not being connected to the internal bias voltages.

code:

  /*Configure GPIO pins : PB0 PB2 PB12, LCD_CAP pins */

  __GPIOB_CLK_ENABLE()

  GPIO_InitStruct.Pin = GPIO_PIN_0|GPIO_PIN_2|GPIO_PIN_12;

  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;

  GPIO_InitStruct.Pull = GPIO_NOPULL;

  HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

// CONFIGURE LCD bias voltages to pins PB0, PB2 & PB12

 __SYSCFG_CLK_ENABLE();

 SYSCFG->PMC |= 0x0000000E;

Has anyone else used these pins?

Thanks!

#syscfg->pmc #lcd_capa #lcd-bias-voltage

[crew]

Posted on January 05, 2016 at 20:44

Is this an internal firmware bug? I have tried everything I can think of to get these LCD bias voltages outside of the chip so that I can decouple them. PB0, PB2 & PB12 are configured as inputs, bits 1,2 &3 of the

SYSCFG->PMC are set as in debug the register shows 'x0000000E'. These are the only prerequisites shown in the manual. This product is finished but this one issue, I need access to these LCD bias voltages as the manual indicates. Is there a workaround? 

[Tesla DeLorean]

Posted on January 05, 2016 at 21:07

Is this an internal firmware bug? 

Really not sure that's the right term here, the only software running is your own. You might want to look over the errata for chip related issues.

This is primarily a user forum, as your question isn't getting any traction here, you might be better served contacting you local ST reps or FAE, and working it out through those channels.