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STM32L152V8 and LCD_CAPA and external decoupling

Question asked by Marmot on Dec 21, 2015
Latest reply on Jan 5, 2016 by Clive One
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.


  /*Configure GPIO pins : PB0 PB2 PB12, LCD_CAP pins */
  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->PMC |= 0x0000000E;

Has anyone else used these pins?